Soft Dollar Arrangements - Additional Information (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Soft Dollar Arrangements [Abstract] | |||
| Soft dollar credits | $ 859 | $ 804 | $ 940 |
| X | ||||||||||
- Definition Soft dollar arrangements. No definition available.
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| X | ||||||||||
- Definition Soft dollar credits. No definition available.
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