CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY (DEFICIT) - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Total
BALANCE at Dec. 31, 2017	$ 10	$ 420,525	$ (360,983)	$ 59,552
BALANCE (in shares) at Dec. 31, 2017	97,203,950
Issuance of common stock for stock option exercises		655		$ 655
Issuance of common stock for stock option exercises (in shares)	378,398			378,398
Issuance of common stock pursuant to the Employee Stock Purchase Plan		2,339		$ 2,339
Issuance of common stock pursuant to the Employee Stock Purchase Plan (in shares)	829,182
Issuance of common stock pursuant to the Employee Stock-Settled Bonus Plan	$ 1	9,621		9,622
Issuance of common stock pursuant to the Employee Stock-Settled Bonus Plan (in shares)	1,973,386
Shares withheld for net settlement of Stock-Settled Bonus Plans		(3,724)		(3,724)
Shares withheld for net settlement of Stock-Settled Bonus Plans (in shares)	(752,564)
Vesting of restricted stock units (in shares)	975,803
Stock-based compensation		6,306		6,306
Net loss			(16,370)	(16,370)
BALANCE at Mar. 31, 2018	$ 11	$ 435,722	$ (377,353)	$ 58,380
BALANCE (in shares) at Mar. 31, 2018	100,608,155