Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Nov. 02, 2015	Dec. 10, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss	$ (15,293)	$ (10,917)	$ (13,001)	$ (11,213)	$ (14,782)	$ (13,938)	$ (8,993)	$ 5,295	$ (50,424)	$ (32,418)	$ (16,068)
Shares used in computing basic and diluted net loss per share									67,671	65,225	62,607
Basic and diluted net loss per share (in USD per share)									$ (0.75)	$ (0.50)	$ (0.26)
Securities excluded from calculations of net loss per share because impact would have been anti-dilutive									2,014	2,325	3,011
Potential effective of dilutive shares									14,767	3,588	3,588
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculations of net loss per share because impact would have been anti-dilutive									1,651	1,822	2,374
Restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculations of net loss per share because impact would have been anti-dilutive									133	321	403
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculations of net loss per share because impact would have been anti-dilutive									230	182	234
2.25% Convertible Senior Notes | Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Convertible notes, stated percentage													2.25%
Convertible notes, face amount													$ 86,300
3.25% Convertible Senior Notes | Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Convertible notes, stated percentage												3.25%
Convertible notes, face amount												$ 125,000