Stockholders' Equity and Stock-based Compensation - Common Stock Equivalents Excluded from the Calculation of Earnings per Share (Details) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net income (loss) per share (in shares)	8,878,938	0
Outstanding common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net income (loss) per share (in shares)	5,783,695	4,402,244
Unvested restricted stock awards and performance stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net income (loss) per share (in shares)	3,731,088	788,125
Shares of common stock expected to be purchased on December 31st under the 2014 ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net income (loss) per share (in shares)	47,074	45,123
Outstanding common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net income (loss) per share (in shares)	0	34,113