Convertible Preferred Stock - Additional Information (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	0 Months Ended
	Mar. 31, 2014	Jun. 07, 2005	Jun. 01, 2009	Dec. 31, 2014	Dec. 31, 2013
Temporary Equity [Line Items]
Total aggregate shares of common stock after conversions	38,065,708
Series G Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares issued		5,391,441		0	5,391,441
Convertible preferred stock, per share		$ 11.00
Aggregate cash purchase price		$ 59.3
Convertible preferred stock, net of issuance costs		59.1
Issuance Costs		0.2
Series H Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares issued			4,124,986	0	4,124,986
Convertible preferred stock, per share			$ 16.69
Aggregate cash purchase price			68.8
Convertible preferred stock, net of issuance costs			63.8
Issuance Costs			$ 5.0