Consolidated Statements Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (shares) at Dec. 31, 2014		39,563
Beginning balance at Dec. 31, 2014	$ 26,311	$ 4	$ 302,379	$ (142)	$ (275,930)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (shares)		172
Exercise of stock options	289		289
Cancellation of shares (shares)		(444)
Cancellation of shares	(1,813)		(1,813)
Release of stock awards (shares)		1,052
Employee stock-based compensation	5,122		5,122
Non-employee stock-based compensation	4		4
Total comprehensive loss	(7,034)			547	(7,581)
Ending balance (shares) at Dec. 31, 2015		40,343
Ending balance at Dec. 31, 2015	22,879	$ 4	305,981	405	(283,511)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (shares)		398
Exercise of stock options	1,034		1,034
Cancellation of shares (shares)		(397)
Cancellation of shares	(1,524)		(1,524)
Release of stock awards (shares)		911
Employee stock-based compensation	5,673		5,673
Total comprehensive loss	(8,963)			(405)	(8,558)
Ending balance (shares) at Dec. 31, 2016		41,255
Ending balance at Dec. 31, 2016	$ 19,099	$ 4	311,164	0	(292,069)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (shares)	86	86
Exercise of stock options	$ 266		266
Cancellation of shares (shares)		(397)
Cancellation of shares	(1,671)		(1,671)
Release of stock awards (shares)		1,096
Employee stock-based compensation	7,048		7,048
Non-employee stock-based compensation	43		43
Issuance of common stock, net of issuance costs (shares)		6,325
Issuance of common stock, net of issuance costs	23,230	$ 1	23,229
Total comprehensive loss	(23,468)			(472)	(22,996)
Ending balance (shares) at Dec. 31, 2017		48,365
Ending balance at Dec. 31, 2017	$ 24,547	$ 5	$ 340,079	$ (472)	$ (315,065)