CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Noncontrolling Interests
Balance at Dec. 31, 2018	$ 84,519	$ 136	$ 863,531	$ (281)	$ (778,867)
Balance (in shares) at Dec. 31, 2018		136,853
Issuance of common stock from public offering, net of offering costs	26,860	$ 6	26,854
Issuance of common stock from public offering, net of offering costs (in shares)		5,648
Issuance of common stock from exercise of stock options, vesting of restricted stock units, and ESPP purchases	3,210	$ 2	3,208
Issuance of common stock from exercise of stock options, vesting of restricted stock units, and ESPP purchases (in shares)		1,790
Stock-based compensation	13,312		13,312
Other comprehensive income (loss)	395			395
Net loss	(71,244)				(71,244)
Balance at Dec. 31, 2019	57,052	$ 144	906,905	114	(850,111)
Balance (in shares) at Dec. 31, 2019		144,291
Issuance of common stock from public offering, net of offering costs	76,272	$ 19	76,253
Issuance of common stock from public offering, net of offering costs (in shares)		19,338
Issuance of common stock from exercise of stock options, vesting of restricted stock units, and ESPP purchases	11,750	$ 5	11,745
Issuance of common stock from exercise of stock options, vesting of restricted stock units, and ESPP purchases (in shares)		4,541
Stock-based compensation	18,029		18,029
Other comprehensive income (loss)	560			560
Net loss	(59,857)				(59,857)
Balance at Dec. 31, 2020	103,806	$ 168	1,012,932	674	(909,968)
Balance (in shares) at Dec. 31, 2020		168,170
Issuance of common stock from public offering, net of offering costs	3,069	$ 1	3,068
Issuance of common stock from public offering, net of offering costs (in shares)		400
Issuance of common stock from exercise of stock options, vesting of restricted stock units, and ESPP purchases	9,370	$ 5	9,365
Issuance of common stock from exercise of stock options, vesting of restricted stock units, and ESPP purchases (in shares)		5,100
Stock-based compensation	23,571		23,571
Other comprehensive income (loss)	(823)			(823)
Equity contribution from noncontrolling interest	1,000					$ 1,000
Net loss	(54,376)				(54,374)	(2)
Balance at Dec. 31, 2021	$ 85,617	$ 174	$ 1,048,936	$ (149)	$ (964,342)	$ 998
Balance (in shares) at Dec. 31, 2021		173,670