Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	At-the-market sales offering	Public offering	Common Stock	Common Stock At-the-market sales offering	Common Stock Public offering	Additional Paid-In Capital	Additional Paid-In Capital At-the-market sales offering	Additional Paid-In Capital Public offering	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance, (shares) at Dec. 31, 2018				110,525,141
Beginning Balance at Dec. 31, 2018	$ 271,410			$ 110			$ 886,740			$ (3,702)	$ (611,738)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(19,259)										(19,259)
Other comprehensive loss, net	(390)									(390)
Recognition of stock-based compensation expense	7,481						7,481
Issuance of common stock to 401(k) plan for employees (shares)				47,347
Issuance of common stock to 401(k) plan for employees	519						519
Issuance of common stock upon exercise of stock options (shares)				146,785
Issuance of common stock upon exercise of stock options	831									831
Restricted stock award grants, net of forfeitures (shares)				259,539
Restricted stock award grants, net of forfeitures	1			$ 1
Issuance of common stock upon vesting of restricted stock units (shares)				233,760
Issuance of common stock upon vesting of restricted stock units	0
Ending Balance, (shares) at Mar. 31, 2019				111,212,572
Ending Balance at Mar. 31, 2019	260,593			$ 111			895,571			(4,092)	(630,997)
Beginning Balance, (shares) at Dec. 31, 2018				110,525,141
Beginning Balance at Dec. 31, 2018	271,410			$ 110			886,740			(3,702)	(611,738)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(73,639)
Ending Balance, (shares) at Sep. 30, 2019				112,988,706
Ending Balance at Sep. 30, 2019	222,763			$ 113			912,558			(4,531)	(685,377)
Beginning Balance, (shares) at Mar. 31, 2019				111,212,572
Beginning Balance at Mar. 31, 2019	260,593			$ 111			895,571			(4,092)	(630,997)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(28,395)										(28,395)
Other comprehensive loss, net	328									328
Recognition of stock-based compensation expense	$ 4,814						4,814
Issuance of common shares, net (shares)	221,529				221,529
Issuance of common shares, net		$ 1,814						$ 1,814
Issuance of common stock to 401(k) plan for employees (shares)				24,382
Issuance of common stock to 401(k) plan for employees	$ 205						205
Issuance of common stock for employee stock purchase plan (shares)				60,606
Issuance of common stock for employee stock purchase plan	444						444
Issuance of common stock upon exercise of stock options (shares)				504,226
Issuance of common stock upon exercise of stock options	3,023						3,023
Restricted stock award grants, net of forfeitures (shares)				651,072
Restricted stock award grants, net of forfeitures	1			$ 1
Issuance of common stock upon vesting of restricted stock units (shares)				10,000
Issuance of common stock upon vesting of restricted stock units	0
Ending Balance, (shares) at Jun. 30, 2019				112,684,387
Ending Balance at Jun. 30, 2019	242,827			$ 112			905,871			(3,764)	(659,392)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(25,985)										(25,985)
Other comprehensive loss, net	(767)									(767)
Recognition of stock-based compensation expense	4,021						4,021
Issuance of common stock to 401(k) plan for employees (shares)				21,454
Issuance of common stock to 401(k) plan for employees	165						165
Issuance of common stock upon exercise of stock options (shares)				364,358
Issuance of common stock upon exercise of stock options	2,499			$ 1			2,498
Restricted stock award grants, net of forfeitures (shares)				(81,493)
Restricted stock award grants, net of forfeitures	0
Refund of SEC fees in connection with an at-the-market sales agreement for our common shares	3						3
Ending Balance, (shares) at Sep. 30, 2019				112,988,706
Ending Balance at Sep. 30, 2019	222,763			$ 113			912,558			(4,531)	(685,377)
Beginning Balance, (shares) at Dec. 31, 2019				113,299,612
Beginning Balance at Dec. 31, 2019	190,393			$ 113			918,205			(3,498)	(724,427)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(40,572)										(40,572)
Other comprehensive loss, net	(1,329)									(1,329)
Recognition of stock-based compensation expense	5,010						5,010
Issuance of common stock to 401(k) plan for employees (shares)				96,959
Issuance of common stock to 401(k) plan for employees	265						265
Restricted stock award grants, net of forfeitures (shares)				1,377,508
Restricted stock award grants, net of forfeitures	1			$ 1
Ending Balance, (shares) at Mar. 31, 2020				114,774,079
Ending Balance at Mar. 31, 2020	153,768			$ 114			923,480			(4,827)	(764,999)
Beginning Balance, (shares) at Dec. 31, 2019				113,299,612
Beginning Balance at Dec. 31, 2019	190,393			$ 113			918,205			(3,498)	(724,427)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(121,109)
Ending Balance, (shares) at Sep. 30, 2020				145,931,172
Ending Balance at Sep. 30, 2020	168,360			$ 146			1,016,474			(2,724)	(845,536)
Beginning Balance, (shares) at Mar. 31, 2020				114,774,079
Beginning Balance at Mar. 31, 2020	153,768			$ 114			923,480			(4,827)	(764,999)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(32,085)										(32,085)
Other comprehensive loss, net	1,573									1,573
Recognition of stock-based compensation expense	$ 3,988						3,988
Issuance of common shares, net (shares)	1,024,286				1,024,286
Issuance of common shares, net		3,071			$ 1			3,070
Issuance of common stock for employee stock purchase plan (shares)				98,362
Issuance of common stock for employee stock purchase plan	$ 282						282
Restricted stock award grants, net of forfeitures (shares)				1,926,385
Restricted stock award grants, net of forfeitures	0			$ 3			(3)
Issuance of common stock upon vesting of restricted stock units (shares)				861
Issuance of common stock upon vesting of restricted stock units	0
Ending Balance, (shares) at Jun. 30, 2020				117,823,973
Ending Balance at Jun. 30, 2020	130,597			$ 118			930,817			(3,254)	(797,084)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(48,452)										(48,452)
Other comprehensive loss, net	530									530
Recognition of stock-based compensation expense	$ 4,108						4,108
Issuance of common shares, net (shares)	2,926,112				2,926,112	24,916,667
Issuance of common shares, net		$ 11,831	$ 69,733		$ 3	$ 25		$ 11,828	$ 69,708
Issuance of common stock upon exercise of stock options (shares)				3,542
Issuance of common stock upon exercise of stock options	$ 13						13
Restricted stock award grants, net of forfeitures (shares)				260,878
Restricted stock award grants, net of forfeitures	0
Issuance of common stock upon vesting of restricted stock units (shares)				0
Issuance of common stock upon vesting of restricted stock units	0
Ending Balance, (shares) at Sep. 30, 2020				145,931,172
Ending Balance at Sep. 30, 2020	$ 168,360			$ 146			$ 1,016,474			$ (2,724)	$ (845,536)