Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | |||
---|---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
Dec. 31, 2016 |
|
Significant Accounting Policies [Line Items] | |||||
Accumulated deficit | $ 252,712 | $ 252,712 | $ 215,979 | ||
Cash, cash equivalents and available-for-sale investments | $ 90,400 | $ 90,400 | |||
Weighted average shares subject to repurchase | 175 | 21,871 | 4,607 | 29,467 | |
Pangu BioPharma [Member] | Hong Kong [Member] | |||||
Significant Accounting Policies [Line Items] | |||||
Majority-owned subsidiary percentage | 98.00% | 98.00% |