Acquisitions - Summary of Pro Forma Information (Detail) - Cortina Asset Management, LLC - USD ($) $ in Thousands  | 
9 Months Ended | |
|---|---|---|
Sep. 30, 2019  | 
Sep. 30, 2018  | 
|
| Business Acquisition [Line Items] | ||
| Revenue | $ 80,508 | $ 84,857 | 
| Net Income | $ 11,797 | $ 16,899 | 
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
  | 
| X | ||||||||||
- Definition The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
  | 
| X | ||||||||||
- Definition The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
  | 
| X | ||||||||||
- Details 
  |