Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Nov. 02, 2015	Dec. 10, 2013
Earnings Per Share [Abstract]
Net loss	$ (24,924,000)	$ (15,245,000)	$ (66,837,000)	$ (47,671,000)	$ (15,293,000)	$ (10,917,000)	$ (13,001,000)	$ (11,213,000)	$ (154,677,000)	$ (50,424,000)	$ (32,418,000)
Shares used in computing basic and diluted net loss per share (in shares)									80,976	67,671	65,225
Basic and diluted net loss per share (in USD per share)	$ (0.30)	$ (0.18)	$ (0.81)	$ (0.62)	$ (0.22)	$ (0.16)	$ (0.19)	$ (0.17)	$ (1.91)	$ (0.75)	$ (0.50)
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 (in shares)									1,747	2,014	2,325
Potential effective of dilutive shares (in shares)									14,767	14,767	3,588
2.25% Convertible Senior Notes | Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Convertible notes, face amount													$ 86,300,000
Convertible notes, stated percentage													2.25%
3.25% Convertible Senior Notes | Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Convertible notes, face amount												$ 125,000,000.0
Convertible notes, stated percentage												3.25%
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 (in shares)									1,248	1,651	1,822
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 (in shares)									129	133	321
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 (in shares)									370	230	182