CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Statement Of Cash Flows [Abstract]
Restricted cash	$ 0	$ 0	$ 100	$ 100
Restricted Cash, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherNoncurrentAssetsMember	us-gaap:OtherNoncurrentAssetsMember	us-gaap:OtherNoncurrentAssetsMember	us-gaap:OtherNoncurrentAssetsMember