Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2018		41,227,530
Beginning balance at Dec. 31, 2018	$ 118,611	$ 41	$ 436,554	$ (317,927)	$ (57)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation expense	2,425		2,425
Exercise of common stock options (in shares)		5,000
Exercise of common stock options	15		15
Issuance of common stock under employee stock purchase plan (in shares)		31,892
Issuance of common stock under employee stock purchase plan	173		173
Foreign currency translation adjustment	3				3
Net loss	(28,874)			(28,874)
Ending balance at Mar. 31, 2019	92,353	$ 41	439,167	(346,801)	(54)
Ending balance (in shares) at Mar. 31, 2019		41,264,422
Beginning balance (in shares) at Dec. 31, 2018		41,227,530
Beginning balance at Dec. 31, 2018	118,611	$ 41	436,554	(317,927)	(57)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(56,251)
Ending balance at Jun. 30, 2019	68,472	$ 41	442,676	(374,178)	(67)
Ending balance (in shares) at Jun. 30, 2019		41,430,918
Beginning balance (in shares) at Mar. 31, 2019		41,264,422
Beginning balance at Mar. 31, 2019	92,353	$ 41	439,167	(346,801)	(54)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation expense	2,716		2,716
Exercise of common stock options (in shares)		88,587
Exercise of common stock options	354		354
Issuance of common stock under employee stock purchase plan (in shares)		77,909
Issuance of common stock under employee stock purchase plan	439		439
Foreign currency translation adjustment	(13)				(13)
Net loss	(27,377)			(27,377)
Ending balance at Jun. 30, 2019	68,472	$ 41	442,676	(374,178)	(67)
Ending balance (in shares) at Jun. 30, 2019		41,430,918
Beginning balance (in shares) at Dec. 31, 2019		45,906,162
Beginning balance at Dec. 31, 2019	61,583	$ 46	489,565	(427,980)	(48)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation expense	2,429		2,429
Foreign currency translation adjustment	(25)				(25)
Net loss	(28,856)			(28,856)
Ending balance at Mar. 31, 2020	35,131	$ 46	491,994	(456,836)	(73)
Ending balance (in shares) at Mar. 31, 2020		45,906,162
Beginning balance (in shares) at Dec. 31, 2019		45,906,162
Beginning balance at Dec. 31, 2019	61,583	$ 46	489,565	(427,980)	(48)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(54,708)
Ending balance at Jun. 30, 2020	12,609	$ 46	495,329	(482,688)	(78)
Ending balance (in shares) at Jun. 30, 2020		45,992,273
Beginning balance (in shares) at Mar. 31, 2020		45,906,162
Beginning balance at Mar. 31, 2020	35,131	$ 46	491,994	(456,836)	(73)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation expense	2,748		2,748
Exercise of common stock options (in shares)		15,806
Exercise of common stock options	71		71
Issuance of common stock under employee stock purchase plan (in shares)		70,305
Issuance of common stock under employee stock purchase plan	516		516
Foreign currency translation adjustment	(5)				(5)
Net loss	(25,852)			(25,852)
Ending balance at Jun. 30, 2020	$ 12,609	$ 46	$ 495,329	$ (482,688)	$ (78)
Ending balance (in shares) at Jun. 30, 2020		45,992,273