Liquidity and Capital Resources (Details) - USD ($) $ in Thousands			1 Months Ended	9 Months Ended
	Sep. 23, 2020	Mar. 16, 2020	Feb. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Liquidity and Capital Resources
Cash and cash equivalents				$ 56,614		$ 11,794
Investments available-for-sale				10,702		14,250
Working capital net				65,200
Accumulated deficit				328,743		$ 306,516
Net cash used in operating activities				$ 21,072	$ 21,954
Common shares sold (in shares)	23,178,809		3,670,212	1,128,608
Proceeds from issuance of common shares, net of issuance costs	$ 32,700		$ 8,000	$ 2,300
Net draw down proceeds		$ 21,200
Remaining amount available for sale				$ 32,300