Furniture, Equipment and Leasehold Improvements, Net - Additional Information (Detail) - USD ($) $ in Thousands  | 
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2018  | 
Jun. 30, 2017  | 
Jun. 30, 2018  | 
Jun. 30, 2017  | 
|
| Property Plant And Equipment [Abstract] | ||||
| Depreciation expense | $ 200 | $ 226 | $ 388 | $ 434 | 
| X | ||||||||||
- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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| X | ||||||||||
- References No definition available. 
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