Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ (Deficit) Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Series 1 redeemable convertible non-voting preferred stock
Balance, beginning of period (in shares) at Dec. 31, 2018		4,424,205	67,746
Balance, beginning of period at Dec. 31, 2018	$ 68,478	$ 442	$ (5,056)	$ 493,784	$ (420,548)	$ (144)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	2,136			2,136
Issuance of common stock upon vesting of restricted stock units (in shares)		2,271
Comprehensive loss	(24,449)				(24,528)	79
Exercise of stock options (in shares)		2,765
Exercise of stock options	70			70
Issuance of common stock in open market transactions, net of issuance costs (in shares)		135,065
Issuance of common stock in open market transactions, net of issuance costs	4,625	$ 14		4,611
Balance, end of period (in shares) at Mar. 31, 2019		4,564,306	67,746
Balance, end of period at Mar. 31, 2019	50,860	$ 456	$ (5,056)	500,601	(445,076)	(65)
Balance, beginning of period (in shares) at Dec. 31, 2018		4,424,205	67,746
Balance, beginning of period at Dec. 31, 2018	68,478	$ 442	$ (5,056)	493,784	(420,548)	(144)
Increase (Decrease) in Stockholders' Equity
Comprehensive loss	(51,426)
Balance, end of period (in shares) at Jun. 30, 2019		4,693,162	67,746
Balance, end of period at Jun. 30, 2019	30,308	$ 469	$ (5,056)	507,013	(472,012)	(106)
Balance, beginning of period (in shares) at Mar. 31, 2019		4,564,306	67,746
Balance, beginning of period at Mar. 31, 2019	50,860	$ 456	$ (5,056)	500,601	(445,076)	(65)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	1,996			1,996
Issuance of common stock upon vesting of restricted stock units (in shares)		585
Comprehensive loss	(26,977)				(26,936)	(41)
Exercise of stock options (in shares)		221
Exercise of stock options	6			6
Issuance of common stock in open market transactions, net of issuance costs (in shares)		124,050
Issuance of common stock in open market transactions, net of issuance costs	4,352	$ 12		4,340
Issuance of common stock - Employee Stock Purchase Plan (in shares)		4,000
Issuance of common stock - Employee Stock Purchase Plan	71	$ 1		70
Balance, end of period (in shares) at Jun. 30, 2019		4,693,162	67,746
Balance, end of period at Jun. 30, 2019	30,308	$ 469	$ (5,056)	507,013	(472,012)	(106)
Preferred stock, beginning balance (in shares) at Dec. 31, 2019							538,000
Preferred stock, beginning balance at Dec. 31, 2019	21,468						$ 21,468
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable preferred stock into common stock (in shares)		40,000					(4,000)
Conversion of redeemable preferred stock into common stock	(160)	$ (1)		(159)			$ 160
Preferred stock, ending balance (in shares) at Mar. 31, 2020							534,000
Preferred stock, ending balance at Mar. 31, 2020							$ 21,308
Balance, beginning of period (in shares) at Dec. 31, 2019		5,076,593	67,746
Balance, beginning of period at Dec. 31, 2019	(26,217)	$ 507	$ (5,056)	511,684	(533,025)	(327)
Increase (Decrease) in Stockholders' Equity
1-for-10 Reverse Stock Split		$ (457)		457
Share-based compensation	1,323			1,323
Issuance of common stock upon vesting of restricted stock units (in shares)		1,045
Comprehensive loss	17,563				17,576	(13)
Balance, end of period (in shares) at Mar. 31, 2020		5,117,638	67,746
Balance, end of period at Mar. 31, 2020	(7,171)	$ 51	$ (5,056)	513,623	(515,449)	(340)
Preferred stock, beginning balance (in shares) at Dec. 31, 2019							538,000
Preferred stock, beginning balance at Dec. 31, 2019	21,468						$ 21,468
Preferred stock, ending balance (in shares) at Jun. 30, 2020							534,000
Preferred stock, ending balance at Jun. 30, 2020	21,308						$ 21,308
Balance, beginning of period (in shares) at Dec. 31, 2019		5,076,593	67,746
Balance, beginning of period at Dec. 31, 2019	(26,217)	$ 507	$ (5,056)	511,684	(533,025)	(327)
Increase (Decrease) in Stockholders' Equity
Comprehensive loss	(25,680)
Balance, end of period (in shares) at Jun. 30, 2020		5,127,525	67,746
Balance, end of period at Jun. 30, 2020	(48,785)	$ 51	$ (5,056)	515,252	(558,643)	(389)
Preferred stock, beginning balance (in shares) at Mar. 31, 2020							534,000
Preferred stock, beginning balance at Mar. 31, 2020							$ 21,308
Preferred stock, ending balance (in shares) at Jun. 30, 2020							534,000
Preferred stock, ending balance at Jun. 30, 2020	21,308						$ 21,308
Balance, beginning of period (in shares) at Mar. 31, 2020		5,117,638	67,746
Balance, beginning of period at Mar. 31, 2020	(7,171)	$ 51	$ (5,056)	513,623	(515,449)	(340)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	1,564			1,564
Issuance of common stock upon vesting of restricted stock units (in shares)		361
Comprehensive loss	(43,243)				(43,194)	(49)
Issuance of common stock - Employee Stock Purchase Plan (in shares)		9,526
Issuance of common stock - Employee Stock Purchase Plan	65			65
Balance, end of period (in shares) at Jun. 30, 2020		5,127,525	67,746
Balance, end of period at Jun. 30, 2020	$ (48,785)	$ 51	$ (5,056)	$ 515,252	$ (558,643)	$ (389)