Condensed Consolidated Statements of Cash Flows (Unaudited) (Parenthetical)  | 
 Sep. 30, 2019  
$ / shares 
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|---|---|
| Class B Common Stock | Cortina Asset Management, LLC | |
| Common stock, par value | $ 0.01 | 
| X | ||||||||||
- Definition Face amount or stated value per share of common stock. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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| X | ||||||||||
- Details 
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| X | ||||||||||
- Details 
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