Net Loss per Share - Calculation of Basic and Diluted EPS for Common Stock (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Table] [Line Items]
Net loss	$ (19,643)	$ (24,281)
Weighted-average shares used to compute basic and diluted net loss per Class A and B share	91,786	26,970
Basic and diluted net loss per share (in usd per share)	$ (0.21)	$ (0.90)
Class A [Member]
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Table] [Line Items]
Net loss	(12,562)	(21,983)
Weighted-average shares used to compute basic and diluted net loss per Class A and B share	58,698	24,417
Basic and diluted net loss per share (in usd per share)	$ (0.21)	$ (0.90)
Class B [Member]
Schedule of Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Table] [Line Items]
Net loss	$ (7,081)	$ (2,298)
Weighted-average shares used to compute basic and diluted net loss per Class A and B share	33,088	2,553
Basic and diluted net loss per share (in usd per share)	$ (0.21)	$ (0.90)