Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning balance (shares) at Dec. 31, 2018		54,065,000
Beginning balance at Dec. 31, 2018	$ 56,306	$ 5	$ 386,775	$ (330,474)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (shares)	529,187	529,000
Exercise of stock options	$ 2,843		2,843
Release of stock awards (shares)		441,000
Employee stock-based compensation	4,051		4,051
Taxes paid related to net share settlement of equity awards (in shares)		(144,000)
Taxes paid related to net share settlement of equity awards	(2,799)		(2,799)
Issuance of common stock, net of issuance costs (shares)		3,049,000
Issuance of common stock, net of issuance costs of $74	49,926	$ 1	49,925
Net loss	(11,643)			(11,643)
Ending balance (shares) at Jun. 30, 2019		57,940,000
Ending balance at Jun. 30, 2019	98,684	$ 6	440,795	(342,117)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Costs incurred in connection with private placement	74
Beginning balance (shares) at Mar. 31, 2019		54,541,000
Beginning balance at Mar. 31, 2019	51,210	$ 5	386,815	(335,610)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (shares)		310,000
Exercise of stock options	2,067		2,067
Release of stock awards (shares)		40,000
Employee stock-based compensation	1,988		1,988
Issuance of common stock, net of issuance costs (shares)		3,049,000
Issuance of common stock, net of issuance costs of $74	49,926	$ 1	49,925
Net loss	(6,507)			(6,507)
Ending balance (shares) at Jun. 30, 2019		57,940,000
Ending balance at Jun. 30, 2019	98,684	$ 6	440,795	(342,117)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Costs incurred in connection with private placement	74
Beginning balance (shares) at Dec. 31, 2019		58,877,000
Beginning balance at Dec. 31, 2019	$ 105,517	$ 6	447,920	(342,409)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (shares)	32,749	32,000
Exercise of stock options	$ 197		197
Release of stock awards (shares)		300,000
Employee stock-based compensation	4,104		4,104
Non-employee stock-based compensation	4		4
Taxes paid related to net share settlement of equity awards (in shares)		(84,000)
Taxes paid related to net share settlement of equity awards	(1,040)		(1,040)
Net loss	(13,996)			(13,996)
Ending balance (shares) at Jun. 30, 2020		59,125,000
Ending balance at Jun. 30, 2020	94,786	$ 6	451,185	(356,405)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Costs incurred in connection with private placement	0
Beginning balance (shares) at Mar. 31, 2020		59,017,000
Beginning balance at Mar. 31, 2020	99,066	$ 6	449,121	(350,061)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (shares)		27,000
Exercise of stock options	158		158
Release of stock awards (shares)		81,000
Employee stock-based compensation	1,935		1,935
Non-employee stock-based compensation	4		4
Taxes paid related to net share settlement of equity awards (in shares)		0
Taxes paid related to net share settlement of equity awards	(33)		(33)
Net loss	(6,344)			(6,344)
Ending balance (shares) at Jun. 30, 2020		59,125,000
Ending balance at Jun. 30, 2020	$ 94,786	$ 6	$ 451,185	$ (356,405)