Intangible Assets - Summary of Intangible Assets (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Finite Lived Intangible Assets [Line Items]      
Cost, beginning balance $ 19,223 $ 19,223  
Acquisition of certain assets of Jamison 5,804    
Cost, ending balance 25,027 19,223 $ 19,223
Accumulated amortization, beginning balance (8,056) (6,634)  
Amortization expense (1,640) (1,422) (1,521)
Accumulated amortization, ending balance (9,696) (8,056) (6,634)
Net book value $ 15,331 11,167  
Minimum      
Finite Lived Intangible Assets [Line Items]      
Useful lives 3 years    
Maximum      
Finite Lived Intangible Assets [Line Items]      
Useful lives 20 years    
Customer Relationships      
Finite Lived Intangible Assets [Line Items]      
Cost, beginning balance $ 17,560 17,560  
Acquisition of certain assets of Jamison 5,000    
Cost, ending balance 22,560 17,560 17,560
Accumulated amortization, beginning balance (6,627) (5,410)  
Amortization expense (1,435) (1,217)  
Accumulated amortization, ending balance (8,062) (6,627) (5,410)
Net book value $ 14,498 $ 10,933  
Customer Relationships | Minimum      
Finite Lived Intangible Assets [Line Items]      
Useful lives 10 years 10 years  
Customer Relationships | Maximum      
Finite Lived Intangible Assets [Line Items]      
Useful lives 20 years 20 years  
Other Intangible Assets      
Finite Lived Intangible Assets [Line Items]      
Cost, beginning balance $ 1,663 $ 1,663  
Acquisition of certain assets of Jamison 804    
Cost, ending balance 2,467 1,663 1,663
Accumulated amortization, beginning balance (1,429) (1,224)  
Amortization expense (205) (205)  
Accumulated amortization, ending balance (1,634) (1,429) $ (1,224)
Net book value $ 833 $ 234  
Other Intangible Assets | Minimum      
Finite Lived Intangible Assets [Line Items]      
Useful lives 3 years 3 years  
Other Intangible Assets | Maximum      
Finite Lived Intangible Assets [Line Items]      
Useful lives 5 years 5 years