Commitments and Contingencies - Additional Information (Detail) |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2017
USD ($)
ExecutiveOfficer
|
Dec. 31, 2016
USD ($)
|
Dec. 31, 2015
USD ($)
|
|
| Other Commitments [Line Items] | |||
| Number of executive officers contained automatic renewal provisions | ExecutiveOfficer | 4 | ||
| Contractual settlement | $ 1,400,000 | ||
| Non-Cancelable operating lease expiration date | Sep. 30, 2021 | ||
| Non-Cancelable lease agreement for office equipment, expiration year | 2022 | ||
| Rent expense under lease arrangements | $ 748,000 | 1,025,000 | $ 1,002,000 |
| Legal settlement received from a service provider | $ 1,100,000 | ||
| Employment Agreements [Member] | |||
| Other Commitments [Line Items] | |||
| Commitment under contracts | $ 6,300,000 | ||