Condensed Consolidated Statements of Shareholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-In Capital	Additional Paid-In Capital Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Beginning balance (in shares) at Dec. 31, 2020			46,779,479
Beginning balance at Dec. 31, 2020	$ (123,659)	$ (86,433)	$ 5	$ 1,222,137	$ (134,450)	$ 21	$ (1,345,822)	$ 48,017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(15,749)						(15,749)
Unrealized gain (loss) from available-for-sale securities	(21)					(21)
Foreign currency gain	0
Vesting of restricted shares (in shares)			202,018
Vesting of restricted shares	0
Exercise of options (in shares)			193,300
Exercise of options	3,764			3,764
Issuance of common stock upon purchase by employee stock purchase plan (in shares)			66,301
Issuance of common stock upon purchase by employee stock purchase plan	678			678
Share-based compensation expense	5,410			5,410
Ending balance (in shares) at Mar. 31, 2021			47,241,098
Ending balance at Mar. 31, 2021	(216,010)		$ 5	1,097,539		0	(1,313,554)
Beginning balance (in shares) at Dec. 31, 2021			47,359,573
Beginning balance at Dec. 31, 2021	(252,304)		$ 5	1,115,672		0	(1,367,981)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(18,276)						(18,276)
Unrealized gain (loss) from available-for-sale securities	0
Foreign currency gain	6					6
Vesting of restricted shares (in shares)			139,056
Vesting of restricted shares	0
Share-based compensation expense related to share-based awards for employee stock purchase plan	113			113
Issuance of common stock upon purchase by employee stock purchase plan (in shares)			66,135
Issuance of common stock upon purchase by employee stock purchase plan	482			482
Share-based compensation expense	4,032			4,032
Ending balance (in shares) at Mar. 31, 2022			47,564,764
Ending balance at Mar. 31, 2022	$ (265,947)		$ 5	$ 1,120,299		$ 6	$ (1,386,257)