Redeemable Convertible Preferred Stock (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 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	2,605,000
Ending Balance, Preferred Stock Issued and Outstanding		197,948,000
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		33,000
Ending Balance, Preferred Stock Issued and Outstanding		2,592,000
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		317,000
Ending Balance, Preferred Stock Issued and Outstanding		23,235,000
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		409,000
Ending Balance, Preferred Stock Issued and Outstanding		25,158,000
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		94,000
Ending Balance, Preferred Stock Issued and Outstanding		5,495,000
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		1,204,000
Ending Balance, Preferred Stock Issued and Outstanding		63,920,000
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		548,000
Ending Balance, Preferred Stock Issued and Outstanding		77,548,000
Redeemable Convertible Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ending Balance, Preferred Stock Issued and Outstanding	$ 0