Convertible Preferred Stock (the "Preferred Stock") (Details) - USD ($)			1 Months Ended	12 Months Ended
	Jul. 07, 2015	Sep. 10, 2014	Aug. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Temporary equity
Number of shares issued upon conversion of convertible stock	25,500,000
Shares Authorized				50,479,286
Shares Outstanding				50,452,939
Common Shares Upon Conversion				25,450,440
Liquidation Preference				$ 117,913,630
Convertible Preferred Stock
Temporary equity
Number of shares issued upon conversion of convertible stock	25,500,000
Shares Outstanding				50,452,939	37,590,286
Number of new shares issued during period				11,329,068
Convertible preferred stock, excluding Series F
Temporary equity
Dividend rate (as a percent)				7.50%
Convertible Preferred Stock Series A
Temporary equity
Shares Authorized				418,634
Shares Outstanding				418,634
Common Shares Upon Conversion				1,628,498
Liquidation Preference				$ 5,232,925
Original Issue Price (in dollars per share)				$ 7.425
Conversion Price (in dollars per share)				$ 1.9090
Number of Shares of Common Stock Issued for each Preferred Share Upon Conversion				3.8900
Convertible Preferred Stock Series A1
Temporary equity
Shares Authorized				53,957
Shares Outstanding				53,957
Common Shares Upon Conversion				282,689
Liquidation Preference				$ 918,955
Original Issue Price (in dollars per share)				$ 10.00
Conversion Price (in dollars per share)				$ 1.9090
Number of Shares of Common Stock Issued for each Preferred Share Upon Conversion				5.2391
Convertible Preferred Stock Series B
Temporary equity
Shares Authorized				263,839
Shares Outstanding				263,839
Common Shares Upon Conversion				1,790,050
Liquidation Preference				$ 5,768,378
Original Issue Price (in dollars per share)				$ 12.95
Conversion Price (in dollars per share)				$ 1.9090
Number of Shares of Common Stock Issued for each Preferred Share Upon Conversion				6.7846
Convertible Preferred Stock Series C1
Temporary equity
Shares Authorized				18,287,483
Shares Outstanding				18,267,759
Common Shares Upon Conversion				7,991,496
Liquidation Preference				$ 15,253,579
Original Issue Price (in dollars per share)				$ 0.835
Conversion Price (in dollars per share)				$ 1.9090
Number of Shares of Common Stock Issued for each Preferred Share Upon Conversion				0.4375
Convertible Preferred Stock Series D
Temporary equity
Shares Authorized				12,339,204
Shares Outstanding				12,339,204
Common Shares Upon Conversion				5,397,962
Liquidation Preference				$ 18,600,005
Original Issue Price (in dollars per share)				$ 1.5074
Conversion Price (in dollars per share)				$ 3.4458
Number of Shares of Common Stock Issued for each Preferred Share Upon Conversion				0.4375
Convertible Preferred Stock Series E
Temporary equity
Shares Authorized				6,227,169
Shares Outstanding				6,227,169
Common Shares Upon Conversion				2,724,165
Liquidation Preference				$ 15,000,005
Original Issue Price (in dollars per share)				$ 2.4088
Conversion Price (in dollars per share)				$ 5.5063
Number of Shares of Common Stock Issued for each Preferred Share Upon Conversion				0.4375
Convertible Preferred Stock Series F
Temporary equity
Shares Authorized				12,889,000
Shares Outstanding				12,882,377
Common Shares Upon Conversion				5,635,580
Liquidation Preference				$ 57,139,783
Accrued and accumulated dividends			$ 13,800,000
Rate at which new series of Preferred stock received in exchange for accrued dividends (in dollars per share)			$ 0.50
Rate at which accrued dividends were converted into new series of preferred stock (in dollars per share)			$ 1.00
Number of new shares issued during period		1,554,000
Original Issue Price (in dollars per share)				$ 4.4355
Conversion Price (in dollars per share)				$ 10.1391
Number of Shares of Common Stock Issued for each Preferred Share Upon Conversion				0.4375