Acquisitions - Summary of Pro Forma Information (Detail) - Cortina Asset Management, LLC $ in Thousands  | 
3 Months Ended | 
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| 
 Mar. 31, 2019  
USD ($) 
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| Business Acquisition [Line Items] | |
| Revenue | $ 25,580 | 
| Net Income | $ 3,678 | 
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- 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. 
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- 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 
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- 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 
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- Details 
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