Consolidated Statements of Operations - USD ($)
shares in Thousands, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Operating expenses                      
Research and development $ 16,731 $ 20,664 $ 16,397 $ 18,192 $ 15,586 $ 15,400 $ 11,940 $ 17,100 $ 71,984 $ 60,025 $ 32,608
General and administrative 5,760 6,752 5,909 5,915 4,622 5,124 7,556 5,181 24,336 22,483 13,505
Total operating expenses 22,491 27,416 22,306 24,107 20,208 20,524 19,496 22,281 96,320 82,508 46,113
Loss from operations (22,491) (27,416) (22,306) (24,107) (20,208) (20,524) (19,496) (22,281) (96,320) (82,508) (46,113)
Interest income 160 120 129 105 51 54 65 49 514 218 132
Other income (expense), net 446 (39) 59 (230) 32 91 (236) 226 236 113 (11,532)
Net loss before provision for income taxes (21,885) (27,335) (22,118) (24,232)         (95,570) (82,177) (57,513)
Provision for income taxes 247               247    
Net loss $ (22,132) $ (27,335) $ (22,118) $ (24,232) (20,125) (20,379) (19,667) (22,006) (95,817) (82,177) (57,513)
Deemed dividend related to beneficial conversion feature of convertible preferred stock                     (25,559)
Net loss attributable to common stockholders         $ (20,125) $ (20,379) $ (19,667) $ (22,006) $ (95,817) $ (82,177) $ (83,072)
Net loss per share- basic and diluted $ (0.64) $ (0.92) $ (0.75) $ (0.82) $ (0.69) $ (0.69) $ (0.67) $ (0.79) $ (3.11) $ (2.84) $ (4.39)
Weighted-average common shares used to compute basic and diluted net loss per share 34,609 29,574 29,489 29,422 29,379 29,354 29,293 27,810 30,784 28,964 18,922