Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Treasury Stock at Cost	Total
Balance at Dec. 31, 2013	$ 3	$ 345,345	$ 12	$ (170,269)	$ (30,110)	$ 144,981
Balance (in shares) at Dec. 31, 2013	30,964,000
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options for cash and vesting of restricted stock units		4,156				4,156
Issuance of common stock upon exercise of stock options for cash and vesting of restricted stock units (in shares)	748,000
Issuance of common stock upon settlement of employee stock purchase plan		4,227				4,227
Issuance of common stock upon settlement of employee stock purchase plan (in shares)	191,000
Issuance of restricted stock to directors in lieu of fees		230				230
Issuance of restricted stock to directors in lieu of fees (in shares)	8,000
Stock-based compensation expense related to employee stock options, restricted stock units and employee stock purchase plan		16,410				16,410
Stock-based compensation expense related to consultant restricted stock units		128				128
Net loss				(24,592)		(24,592)
Unrealized gain (loss) on investments, net of tax			(27)			(27)
Balance at Dec. 31, 2014	$ 3	370,496	(15)	(194,861)	(30,110)	145,513
Balance (in shares) at Dec. 31, 2014	31,911,000
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options for cash and vesting of restricted stock units		3,664				3,664
Issuance of common stock upon exercise of stock options for cash and vesting of restricted stock units (in shares)	678,000
Issuance of common stock upon settlement of employee stock purchase plan		4,694				4,694
Issuance of common stock upon settlement of employee stock purchase plan (in shares)	204,000
Issuance of restricted stock to directors in lieu of fees		200				200
Issuance of restricted stock to directors in lieu of fees (in shares)	7,000
Stock-based compensation expense related to employee stock options, restricted stock units and employee stock purchase plan		16,005				16,005
Net loss				(33,308)		(33,308)
Unrealized gain (loss) on investments, net of tax			2,767			2,767
Balance at Dec. 31, 2015	$ 3	395,059	2,752	(228,169)	(30,110)	$ 139,535
Balance (in shares) at Dec. 31, 2015	32,800,000					32,800,428
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options for cash and vesting of restricted stock units		8,385				$ 8,385
Issuance of common stock upon exercise of stock options for cash and vesting of restricted stock units (in shares)	799,000
Issuance of common stock upon settlement of employee stock purchase plan		5,155				5,155
Issuance of common stock upon settlement of employee stock purchase plan (in shares)	226,000
Issuance of restricted stock to directors in lieu of fees		200				200
Issuance of restricted stock to directors in lieu of fees (in shares)	7,000
Stock-based compensation expense related to employee stock options, restricted stock units and employee stock purchase plan		18,303				18,303
Net loss				(13,919)		(13,919)
Unrealized gain (loss) on investments, net of tax			300			300
Reclassification adjustment for net gain on sale of equity securities included in net loss			(1,854)			(1,854)
Balance at Dec. 31, 2016	$ 3	$ 427,102	$ 1,198	$ (242,088)	$ (30,110)	$ 156,105
Balance (in shares) at Dec. 31, 2016	33,832,000					33,831,998