CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	Convertible Senior Notes Due 2019	Convertible Senior Notes Due 2019 Additional Paid-In Capital	Convertible Senior Notes Due 2022	Convertible Senior Notes Due 2022 Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity
Cumulative effect adjustment of the adoption of Accounting Standards Update 2016-09 (Note 2)			$ 287	$ (287)
Balances (in shares) at Dec. 31, 2016		37,481,000
Balances at Dec. 31, 2016	$ 218,976	$ 37	565,207	(346,238)	$ (30)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)		459,000
Exercise of stock options	5,304	$ 1	5,303
Vested restricted stock units (in shares)		99,000
Vested restricted stock units	$ 0	$ 0
Shares issued under employee stock purchase plan (in shares)	35,745	36,000
Shares issued under employee stock purchase plan	$ 1,056		1,056
Stock-based compensation	23,407		23,407
Issuance of common stock upon conversion of 2019 convertible senior notes (in shares)		2,490,000
Issuance of common stock upon conversion of 2019 convertible senior notes	120,960	$ 3	120,957
Retirement of equity component of 2019 convertible senior notes						$ (126,328)	$ (126,328)	$ 68,668	$ 68,668
Net unrealized gain (loss) on investments	(37)				(37)
Net loss	(47,206)			(47,206)
Balances (in shares) at Sep. 30, 2017		40,565,000
Balances at Sep. 30, 2017	$ 264,800	$ 41	$ 658,557	$ (393,731)	$ (67)