Property and Equipment, Net - Additional Information (Detail) - USD ($) |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
Property Plant And Equipment [Abstract] | |||
Depreciation and amortization expense related to property plant and equipment | $ 95,000 | ||
Depreciation and amortization expense | 129,000 | $ 232,000 | $ 325,000 |
Disposal of property and equipment | 210,000 | 12,000 | $ 0 |
Proceeds from property and equipment | $ 0 | 0 | |
Loss on disposal of property and equipment | $ (12,000) |