Business, Liquidity and Capital Resources (Details) - Capital Resources and Management Plans [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Business, Liquidity and Capital Resources (Details) [Line Items]
Cash and cash equivalents	$ 58,201		$ 168,598
Investments in marketable debt securities	97,000		$ 0
Net losses	13,465	$ (10,060)
Net cash used in operating activities		$ 11,920
Non-cash stock-based compensation charges	$ 2,740