Redeemable Convertible Preferred Stock (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance, Preferred Stock Issued and Outstanding				$ 118,343,000
Issuance of preferred stock				77,000,000
Accretion of dividends on preferred stock	$ 0	$ 3,596,000	$ 0	6,200,000
Ending Balance, Preferred Stock Issued and Outstanding		201,543,000		201,543,000
Series A [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance, Preferred Stock Issued and Outstanding				2,559,000
Issuance of preferred stock				0
Accretion of dividends on preferred stock				65,000
Ending Balance, Preferred Stock Issued and Outstanding		2,624,000		2,624,000
Series B [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance, Preferred Stock Issued and Outstanding				22,918,000
Issuance of preferred stock				0
Accretion of dividends on preferred stock				634,000
Ending Balance, Preferred Stock Issued and Outstanding		23,552,000		23,552,000
Series C [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance, Preferred Stock Issued and Outstanding				24,749,000
Issuance of preferred stock				0
Accretion of dividends on preferred stock				818,000
Ending Balance, Preferred Stock Issued and Outstanding		25,567,000		25,567,000
Series C-1 [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance, Preferred Stock Issued and Outstanding				5,401,000
Issuance of preferred stock				0
Accretion of dividends on preferred stock				188,000
Ending Balance, Preferred Stock Issued and Outstanding		5,589,000		5,589,000
Series D [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance, Preferred Stock Issued and Outstanding				62,716,000
Issuance of preferred stock				0
Accretion of dividends on preferred stock				2,407,000
Ending Balance, Preferred Stock Issued and Outstanding		65,123,000		65,123,000
Series E [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance, Preferred Stock Issued and Outstanding				0
Issuance of preferred stock				77,000,000
Accretion of dividends on preferred stock				2,088,000
Ending Balance, Preferred Stock Issued and Outstanding		$ 79,088,000		$ 79,088,000
Redeemable Convertible Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ending Balance, Preferred Stock Issued and Outstanding	$ 0		$ 0