| Schedule of computation of basic and diluted earnings per share | 
 
		
			
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						2015 
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				 | 
				
					 
						  
				 | 
				
					 
						2014 
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				 | 
				
					 
						  
				 | 
				
					 
						2013 
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				| 
					 
						Basic earnings per common share 
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				| 
					 
						Net income  
				 | 
				
					 
						$ 
				 | 
				
44,176
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
39,961
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
11,639
				 | 
			 
			
				| 
					 
						Less income allocated to participating securities 
				 | 
				
					 
						  
				 | 
				
604
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
609
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
179
				 | 
			 
			
				| 
					 
						Net income allocated to common shareholders 
				 | 
				
					 
						$ 
				 | 
				
43,572
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
39,352
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
11,460
				 | 
			 
			
				| 
					 
						Weighted average common shares outstanding 
				 | 
				
					 
						  
				 | 
				
22,329,044
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
22,168,500
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
22,029,374
				 | 
			 
			
				| 
					 
						  
				 | 
				
					 
						$ 
				 | 
				
1.95
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
1.78
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
0.52
				 | 
			 
			
				| 
					 
						Earnings per common share assuming dilution 
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				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
			 
			
				| 
					 
						Net income  
				 | 
				
					 
						$ 
				 | 
				
44,176
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
39,961
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
11,639
				 | 
			 
			
				| 
					 
						Less income allocated to participating securities 
				 | 
				
					 
						  
				 | 
				
604
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
609
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
179
				 | 
			 
			
				| 
					 
						Net income allocated to common shareholders 
				 | 
				
					 
						$ 
				 | 
				
43,572
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
39,352
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
11,460
				 | 
			 
			
				| 
					 
						Weighted average common shares outstanding 
				 | 
				
					 
						  
				 | 
				
22,329,044
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
22,168,500
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
22,029,374
				 | 
			 
			
				| 
					 
						Incremental shares applicable to stock based compensation 
				 | 
				
					 
						  
				 | 
				
12,731
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
20,346
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
37,800
				 | 
			 
			
				| 
					 
						Weighted average common shares assuming dilution 
				 | 
				
					 
						  
				 | 
				
22,341,775
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
22,188,846
				 | 
				
					 
						  
				 | 
				
					 
						  
				 | 
				
22,067,174
				 | 
			 
			
				| 
					 
						  
				 | 
				
					 
						$ 
				 | 
				
1.94
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
1.77
				 | 
				
					 
						  
				 | 
				
					 
						$ 
				 | 
				
0.51
				 | 
			 
		  
		
			 
		 
 
  
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