Condensed Consolidated Statements of Stockholders' 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, 2019			46,189,870
Beginning balance at Dec. 31, 2019	$ (42,279)		$ 5	$ 1,194,327		$ 3	$ (1,236,614)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(81,534)						(81,534)
Unrealized gain(loss) from available-for-sale securities	105					105
Vesting of restricted shares (in shares)			203,324
Vesting of restricted shares	0
Issuance of common stock upon purchase by employee stock purchase plan (in shares)			55,297
Issuance of common stock upon purchase by employee stock purchase plan	990			990
Share-based compensation expense	13,299			13,299
Ending balance (in shares) at Jun. 30, 2020			46,448,491
Ending balance at Jun. 30, 2020	(109,419)		$ 5	1,208,616		108	(1,318,148)
Beginning balance (in shares) at Dec. 31, 2019			46,189,870
Beginning balance at Dec. 31, 2019	(42,279)		$ 5	1,194,327		3	(1,236,614)
Ending balance (in shares) at Dec. 31, 2020			46,779,479
Ending 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]
Accounting Standards Update [Extensible List]	Accounting Standards Update 2020-06
Beginning balance (in shares) at Mar. 31, 2020			46,387,437
Beginning balance at Mar. 31, 2020	$ (74,153)		$ 5	1,200,776		(666)	(1,274,268)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(43,880)						(43,880)
Unrealized gain(loss) from available-for-sale securities	774					774
Vesting of restricted shares (in shares)			61,054
Vesting of restricted shares	0
Share-based compensation expense	7,840			7,840
Ending balance (in shares) at Jun. 30, 2020			46,448,491
Ending balance at Jun. 30, 2020	(109,419)		$ 5	1,208,616		108	(1,318,148)
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	(32,559)						(32,559)
Unrealized gain(loss) from available-for-sale securities	(21)					(21)
Vesting of restricted shares (in shares)			213,639
Vesting of restricted shares	0
Exercise of options (in shares)			195,675
Exercise of options	3,804			3,804
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	11,113			11,113
Ending balance (in shares) at Jun. 30, 2021			47,255,094
Ending balance at Jun. 30, 2021	(227,077)		$ 5	1,103,282		0	(1,330,364)
Beginning balance (in shares) at Mar. 31, 2021			47,241,098
Beginning balance at Mar. 31, 2021	(216,010)		$ 5	1,097,539		0	(1,313,554)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(16,810)						(16,810)
Unrealized gain(loss) from available-for-sale securities	0
Vesting of restricted shares (in shares)			11,621
Vesting of restricted shares	0
Exercise of options (in shares)			2,375
Exercise of options	40			40
Share-based compensation expense	5,703			5,703
Ending balance (in shares) at Jun. 30, 2021			47,255,094
Ending balance at Jun. 30, 2021	$ (227,077)		$ 5	$ 1,103,282		$ 0	$ (1,330,364)