Net Loss Per Share - Anti-Dilutive Common Stock Equivalents Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share Basic [Line Items]
Anti-dilutive common stock equivalents excluded from computation of diluted net loss per share	2,534,622	16,219,758	10,450,077
Convertible Preferred Stock (on an as-if-converted basis)
Earnings Per Share Basic [Line Items]
Anti-dilutive common stock equivalents excluded from computation of diluted net loss per share		13,820,301	9,447,378
Stock Options to Purchase Common Stock
Earnings Per Share Basic [Line Items]
Anti-dilutive common stock equivalents excluded from computation of diluted net loss per share	2,534,622	2,303,862	784,790
Restricted Stock Subject to Future Vesting
Earnings Per Share Basic [Line Items]
Anti-dilutive common stock equivalents excluded from computation of diluted net loss per share		95,595	217,909