Income Taxes (Tables)
   | 
12 Months Ended | 
Dec. 31, 2017  | 
| Income Taxes | 
 
 | 
| Schedule of components of provision for income tax expense (benefit) | 
 
		
			
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						Year ended December 31  
				 | 
			 
			
				| 
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						2017 
				 | 
				
					 
						  
				 | 
				
					 
						2016 
				 | 
				
					 
						  
				 | 
				
					 
						2015 
				 | 
			 
			
				| 
					 
						Current: 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
			 
			
				| 
					 
						Federal 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 11,897 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 16,664 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 15,298 
				 | 
			 
			
				| 
					 
						State 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 988 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 1,866 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 2,057 
				 | 
			 
			
				| 
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 12,885 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 18,530 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 17,355 
				 | 
			 
			
				| 
					 
						Deferred: 
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				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
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				 | 
				
					 
						  
				 | 
			 
			
				| 
					 
						Federal 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (17,264) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
4,930
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
6,103
				 | 
			 
			
				| 
					 
						State 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 1,970 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 1,227 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (1,371) 
				 | 
			 
			
				| 
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
(15,294)
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
6,157
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				 | 
				
					 
						  
				 | 
				
4,732
				 | 
			 
			
				| 
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
(2,409)
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
24,687
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
22,087
				 | 
			 
		  
		
			 
		 
   
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| Schedule of reconciliation of income tax expense computed at the federal statutory rate to the provision for income taxes | 
 
		
			
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				| 
					 
						  
				 | 
				
					 
						2017 
				 | 
				
					 
						  
				 | 
				
					 
						2016 
				 | 
				
					 
						  
				 | 
				
					 
						2015 
				 | 
			 
			
				| 
					 
						Federal income tax expense at statutory rate 
				 | 
				
					 
						$ 
				 | 
				
					 
						 18,520 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 22,294 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 23,192 
				 | 
			 
			
				| 
					 
						State taxes, net of federal benefit 
				 | 
				
					 
						  
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						 1,539 
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				 | 
				
					 
						  
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						 2,547 
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				 | 
				
					 
						  
				 | 
				
					 
						 1,077 
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				| 
					 
						Valuation allowance changes 
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						  - 
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				 | 
				
					 
						  
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						 (7) 
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						 (1,028) 
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				| 
					 
						Change in uncertain tax positions, net 
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						 1,043 
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						 50 
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						 43 
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				| 
					 
						Research and development credit 
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						 (160) 
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						 (274) 
				 | 
				
					 
						  
				 | 
				
					 
						  
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						 (241) 
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				| 
					 
						State rate change 
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						 240 
				 | 
				
					 
						  
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						 64 
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				 | 
				
					 
						  
				 | 
				
					 
						 (30) 
				 | 
			 
			
				| 
					 
						Manufacturing tax benefits 
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				 | 
				
					 
						 (933) 
				 | 
				
					 
						  
				 | 
				
					 
						  
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						 (1,248) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (1,302) 
				 | 
			 
			
				| 
					 
						Prior period adjustments 
				 | 
				
					 
						  
				 | 
				
					 
						  - 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 1,096 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  - 
				 | 
			 
			
				| 
					 
						Federal deferred rate change 
				 | 
				
					 
						  
				 | 
				
					 
						 (22,452) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  - 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  - 
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				| 
					 
						Other 
				 | 
				
					 
						  
				 | 
				
					 
						 (206) 
				 | 
				
					 
						  
				 | 
				
					 
						  
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						 165 
				 | 
				
					 
						  
				 | 
				
					 
						  
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						 376 
				 | 
			 
			
				| 
					 
						  
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						$ 
				 | 
				
(2,409)
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						$ 
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24,687
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
22,087
				 | 
			 
		  
		
			 
		 
   
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| Schedule of significant components of deferred tax liabilities and assets | 
 
		
			
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						December 31,  
				 | 
			 
			
				| 
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						2017 
				 | 
				
					 
						  
				 | 
				
					 
						2016 
				 | 
			 
			
				| 
					 
						Deferred tax assets: 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
			 
			
				| 
					 
						Allowance for doubtful accounts 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 259 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 393 
				 | 
			 
			
				| 
					 
						Inventory reserves 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 967 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 1,111 
				 | 
			 
			
				| 
					 
						Warranty liability 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 1,421 
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				 | 
				
					 
						  
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						 2,244 
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				| 
					 
						Deferred compensation 
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				 | 
				
					 
						  
				 | 
				
					 
						 781 
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				 | 
				
					 
						  
				 | 
				
					 
						 548 
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				| 
					 
						Earnout liabilities 
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				 | 
				
					 
						  
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						 694 
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				 | 
				
					 
						  
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						 242 
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				| 
					 
						Pension and retiree health benefit obligations 
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				 | 
				
					 
						  
				 | 
				
					 
						 3,242 
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				 | 
				
					 
						  
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						 5,432 
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				| 
					 
						Accrued vacation 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 656 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 866 
				 | 
			 
			
				| 
					 
						Medical claims reserve 
				 | 
				
					 
						  
				 | 
				
					 
						  
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						 189 
				 | 
				
					 
						  
				 | 
				
					 
						  
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						 72 
				 | 
			 
			
				| 
					 
						State net operating losses 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 3,386 
				 | 
				
					 
						  
				 | 
				
					 
						  
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						 2,853 
				 | 
			 
			
				| 
					 
						Other accrued liabilities 
				 | 
				
					 
						  
				 | 
				
					 
						  
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						 2,092 
				 | 
				
					 
						  
				 | 
				
					 
						  
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						 2,967 
				 | 
			 
			
				| 
					 
						Valuation allowance for state net operating losses 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (777) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (640) 
				 | 
			 
			
				| 
					 
						Total deferred tax assets 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
12,910
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
16,088
				 | 
			 
			
				| 
					 
						Deferred tax liabilities: 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
			 
			
				| 
					 
						Tax deductible goodwill and other intangibles 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (47,163) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (63,324) 
				 | 
			 
			
				| 
					 
						Accelerated depreciation 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (5,084) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (7,176) 
				 | 
			 
			
				| 
					 
						Other 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 68 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (151) 
				 | 
			 
			
				| 
					 
						Total deferred tax liabilities 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (52,179) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (70,651) 
				 | 
			 
			
				| 
					 
						Net deferred tax liabilities 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 (39,269) 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 (54,563) 
				 | 
			 
		  
		
			 
		 
   
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| Schedule of reconciliation of the beginning and ending liability for uncertain tax positions | 
 
		
			
				| 
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
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				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
			 
			
				| 
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
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				| 
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						2017 
				 | 
				
					 
						  
				 | 
				
					 
						2016 
				 | 
				
					 
						  
				 | 
				
					 
						2015 
				 | 
			 
			
				| 
					 
						Balance at beginning of year 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
2,361
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
490
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
464
				 | 
			 
			
				| 
					 
						Increases for tax positions taken in the current year 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
97
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
73
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
26
				 | 
			 
			
				| 
					 
						Increases for tax positions taken in the prior years 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
1,602
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
1,809
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  - 
				 | 
			 
			
				| 
					 
						Decreases due to settlements with taxing authorities 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (8) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (11) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  - 
				 | 
			 
			
				| 
					 
						Decreases due to lapses in the statute of limitations 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						 (521) 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  - 
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  - 
				 | 
			 
			
				| 
					 
						Balance at the end of year 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 3,531 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 2,361 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 490 
				 | 
			 
		  
		
			 
		 
   
 |