Summary of Significant Accounting Policies - Summary of Basic and Diluted Net Loss per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Nov. 15, 2020	Jun. 01, 2019	Feb. 28, 2018	Feb. 15, 2018
Numerator:
Net loss	$ (112,746)	$ (137,620)	$ (70,877)
Denominator:
Weighted-average common shares outstanding, basic (in shares)	56,394	52,019	46,198
Weighted-average common shares outstanding, diluted (in shares)	56,394	52,019	46,198
Net loss per common share, basic (usd per share)	$ (2.00)	$ (2.65)	$ (1.53)
Net loss per common share, diluted (usd per share)	$ (2.00)	$ (2.65)	$ (1.53)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,754	3,206	4,692
Warrant strike price (in dollars per share)	$ 78.75					$ 78.75
Convertible Senior Notes Due February 2023 | Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion price (in dollars per share)						$ 57.38	$ 57.38
Convertible Notes Due November 2025 | Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion price (in dollars per share)				$ 140.14
Convertible Senior Notes Due June 2026 | Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion price (in dollars per share)					$ 88.61
Stock options, restricted stock units, and market stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,264	2,797	3,805
Shares related to the 2023 Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	80	298	887
Shares subject to warrants related to the issuance of the 2023 Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	39	96	0
Shares related to the 2026 Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	371	15	0