Business, Liquidity and Capital Resources (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Business, Liquidity and Capital Resources (Details) [Line Items]
Cash and cash equivalents	$ 46,836	$ 29,971	$ 46,836	$ 29,971	$ 168,598
Net losses	(12,782)	(7,140)	(26,247)	(17,200)
Non-cash stock-based compensation charges	2,998	1,829	5,738	$ 4,627
Liquidity, Capital Resources and Management Plans [Member]
Business, Liquidity and Capital Resources (Details) [Line Items]
Cash and cash equivalents	145,044		145,044		$ 168,598
Net losses	$ 12,782	$ (7,140)
Net cash used in operating activities			21,394
Non-cash stock-based compensation charges			$ 5,738