| Schedule of quarterly financial information (unaudited) | 
 
		
			
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						2017 
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						First 
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						Second 
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						Third 
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						Fourth 
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						Net sales 
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						$ 
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						 72,248 
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						$ 
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						 139,371 
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						$ 
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						 125,339 
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						$ 
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						 137,969 
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						Gross profit 
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						$ 
				 | 
				
					 
						 17,187 
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						$ 
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						 45,033 
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						$ 
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						 36,055 
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						$ 
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						 44,811 
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						Income (loss) before taxes 
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						$ 
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						 (5,971) 
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						$ 
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						 22,354 
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						$ 
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						 15,081 
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						$ 
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						 21,451 
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						Net income (loss) 
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						$ 
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						 (3,277) 
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						$ 
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						 14,746 
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						$ 
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						 9,327 
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						$ 
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						 34,528 
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						Basic net earnings (loss) per common share attributable to common shareholders 
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						$ 
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						 (0.14) 
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						$ 
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						 0.64 
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						$ 
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						 0.41 
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						$ 
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						 1.51 
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						Earnings (loss) per common share assuming dilution attributable to common shareholders 
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						$ 
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						 (0.14) 
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						$ 
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						 0.64 
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						$ 
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						 0.40 
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						$ 
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						 1.50 
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						Dividends per share 
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						$ 
				 | 
				
					 
						 0.24 
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						$ 
				 | 
				
					 
						 0.24 
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						$ 
				 | 
				
					 
						 0.24 
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						$ 
				 | 
				
					 
						 0.24 
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				 | 
			 
		  
		
			 
		 
		
			Results for the year ended December 31, 2016 include Dejana which was purchased on July 15, 2016. Additionally, the first quarter of 2016 includes the impact of litigation proceeds of $10,050.
		 
		
			
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						2016 
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						First 
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						Second 
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						Third 
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						Fourth 
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						Net sales 
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						$ 
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						 48,789 
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						$ 
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						 113,763 
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						$ 
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						 123,573 
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						$ 
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						 130,143 
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						Gross profit 
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						$ 
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						 14,131 
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						$ 
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						 41,521 
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						$ 
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						 36,644 
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						$ 
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						 41,678 
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						Income before taxes 
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						$ 
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						 8,606 
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						$ 
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						 25,551 
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						$ 
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						 11,873 
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						$ 
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						 17,666 
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						Net income  
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						$ 
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						 5,278 
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						$ 
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						 16,328 
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						$ 
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						 7,302 
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						$ 
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						 10,101 
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						Basic net earnings per common share attributable to common shareholders 
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						$ 
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						 0.23 
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						$ 
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						 0.72 
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						$ 
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						 0.32 
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						$ 
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						 0.44 
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						Earnings per common share assuming dilution attributable to common shareholders 
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						$ 
				 | 
				
					 
						 0.23 
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						$ 
				 | 
				
					 
						 0.71 
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						$ 
				 | 
				
					 
						 0.32 
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						$ 
				 | 
				
					 
						 0.44 
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						Dividends per share 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 0.24 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 0.24 
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
					 
						 0.24 
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				 | 
				
					 
						$ 
				 | 
				
					 
						 0.24 
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