Selected Quarterly Financial Information (Unaudited) - Schedule of Selected Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2016 |
Sep. 30, 2016 |
Jun. 30, 2016 |
Mar. 31, 2016 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Quarterly Financial Information Disclosure [Abstract] | |||||||||||
| License and other revenue | $ 1,534 | $ 0 | $ 3 | $ 68 | $ 47 | $ 48 | $ 59 | $ 1,605 | $ 154 | $ 250 | |
| Total operating expenses | 40,986 | 31,055 | 29,755 | 30,347 | 27,212 | 25,790 | 30,535 | $ 27,349 | 132,143 | 110,886 | 119,326 |
| Loss from operations | (39,452) | (31,055) | (29,752) | (30,279) | (27,165) | (25,742) | (30,476) | (27,349) | (130,538) | (110,732) | (119,076) |
| Total other income (expense) | 421 | 428 | 383 | 385 | 369 | 317 | 318 | 290 | (81) | 10 | (2) |
| Net loss | $ (39,040) | $ (30,640) | $ (29,387) | $ (29,917) | $ (26,935) | $ (25,425) | $ (30,158) | $ (27,059) | $ (128,984) | $ (109,577) | $ (118,181) |
| Net loss per share, basic and diluted | $ (0.80) | $ (0.65) | $ (0.64) | $ (0.71) | $ (0.65) | $ (0.69) | $ (0.84) | $ (0.75) | $ (2.81) | $ (2.92) | $ (3.32) |