Soft Dollar Arrangements - Additional Information (Detail) - USD ($) $ in Thousands  | 
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2019  | 
Sep. 30, 2018  | 
Sep. 30, 2019  | 
Sep. 30, 2018  | 
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| Soft Dollar Arrangements [Abstract] | ||||
| Soft dollar credits | $ 209 | $ 193 | $ 554 | $ 579 | 
| X | ||||||||||
- Definition Soft dollar arrangements. No definition available. 
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| X | ||||||||||
- Definition Soft dollar credits. No definition available. 
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