Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.3
Intangible Assets, Net - Summary of Intangible Assets (Detail) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Dec. 31, 2017
Cost of intangible assets gross $ 46,527   $ 46,527   $ 25,027 $ 25,027
Accumulated amortization, beginning balance     (15,134) $ (13,449) (13,449)  
Amortization expense (705) $ (420) (1,401) (1,265) (1,685)  
Accumulated amortization, ending balance (16,535)   (16,535)   (15,134)  
Net book value 29,992   $ 29,992   9,893  
Minimum            
Useful lives     3 years      
Maximum            
Useful lives     20 years      
Cortina Asset Management, LLC            
Acquisition of Cortina     $ 21,500      
Customer Relationships            
Cost of intangible assets gross 44,060   44,060   22,560 22,560
Accumulated amortization, beginning balance     (12,887) (11,367) (11,367)  
Amortization expense     (1,280)   (1,520)  
Accumulated amortization, ending balance (14,167)   (14,167)   (12,887)  
Net book value 29,893   $ 29,893   $ 9,673  
Customer Relationships | Minimum            
Useful lives     10 years   10 years  
Customer Relationships | Maximum            
Useful lives     20 years   20 years  
Customer Relationships | Cortina Asset Management, LLC            
Acquisition of Cortina     $ 21,500      
Other Intangible Assets            
Cost of intangible assets gross 2,467   2,467   $ 2,467 $ 2,467
Accumulated amortization, beginning balance     (2,247) $ (2,082) (2,082)  
Amortization expense     (121)   (165)  
Accumulated amortization, ending balance (2,368)   (2,368)   (2,247)  
Net book value $ 99   $ 99   $ 220  
Other Intangible Assets | Minimum            
Useful lives     3 years   3 years  
Other Intangible Assets | Maximum            
Useful lives     5 years   5 years