Net Loss per Share (EPS) (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
Basic and diluted loss per share:
Net loss	$ (22,960)	$ (17,630)	$ (19,681)	$ (10,004)	$ 1,254	$ 3,724	$ (514)	$ (9,616)	$ (70,275)	$ (5,152)	$ (37,110)
Net loss attributable to common shares, basic and diluted									$ (70,275)	$ (5,152)	$ (37,110)
Weighted-average common shares outstanding									27,687	6,670	6,093
Less: weighted-average unvested common shares subject to repurchase									(1,483)	(1,870)	(2,252)
Weighted-average number of shares used in computing net loss per share, basic and diluted									26,204	4,800	3,841
Basic and diluted net loss per share (in dollars per share)	$ (0.47)	$ (0.39)	$ (3.58)	$ (1.89)					$ (2.68)	$ (1.07)	$ (9.66)