Basis of Presentation and Significant Accounting Policies - Computation of Net Loss per Common Share (Details) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022 shares	Mar. 31, 2021 USD ($) shares
Computation of Net Loss per Common Share
Options outstanding to purchase common stock, shares issuable under the employee stock purchase plan, and unvested restricted stock/units at end of period	27,012	21,320
Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock/units	1,981	3,553
Shares issuable upon conversion of convertible notes at end of period (in shares) | $		501
Common stock equivalents under if-converted method for convertible notes (in shares)		501