Quarterly report pursuant to Section 13 or 15(d)

Intangible Assets, Net - Summary of Intangible Assets (Detail)

v3.19.1
Intangible Assets, Net - Summary of Intangible Assets (Detail) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Cost of intangible assets gross $ 25,027   $ 25,027 $ 25,027
Accumulated amortization, beginning balance (15,134) $ (13,449) (13,449)  
Amortization expense (348) (425) (1,685)  
Accumulated amortization, ending balance (15,482)   (15,134)  
Net book value $ 9,545   9,893  
Minimum        
Useful lives 3 years      
Maximum        
Useful lives 20 years      
Customer Relationships        
Cost of intangible assets gross $ 22,560   22,560 22,560
Accumulated amortization, beginning balance (12,887) (11,367) (11,367)  
Amortization expense (308)   (1,520)  
Accumulated amortization, ending balance (13,195)   (12,887)  
Net book value $ 9,365   $ 9,673  
Customer Relationships | Minimum        
Useful lives 10 years   10 years  
Customer Relationships | Maximum        
Useful lives 20 years   20 years  
Other Intangible Assets        
Cost of intangible assets gross $ 2,467   $ 2,467 $ 2,467
Accumulated amortization, beginning balance (2,247) $ (2,082) (2,082)  
Amortization expense (40)   (165)  
Accumulated amortization, ending balance (2,287)   (2,247)  
Net book value $ 180   $ 220  
Other Intangible Assets | Minimum        
Useful lives 3 years   3 years  
Other Intangible Assets | Maximum        
Useful lives 5 years   5 years