Warrants (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Jul. 16, 2012	Jun. 28, 2012	Jun. 07, 2012	Jun. 02, 2012	May 24, 2012	May 14, 2012
Maximum
Class of Warrant or Right [Line Items]
Warrant Exercise Price	7.50
Minimum
Class of Warrant or Right [Line Items]
Warrant Exercise Price	6.25
Warrant Liability
Class of Warrant or Right [Line Items]
Warrants issued to purchase common stock	6,033,050	6,033,050
Issued in Series A, B and D Preferred Stock offering | Warrant Liability
Class of Warrant or Right [Line Items]
Warrants issued to purchase common stock	2,247,118	2,247,118
Warrant Exercise Price	6.25
Issued in March 2010 financing | Warrant Liability
Class of Warrant or Right [Line Items]
Warrants issued to purchase common stock	393,416	393,416
Warrant Exercise Price	6.25
Expiration Dates	Mar. 01, 2016
Issued in June 2011 financing | Warrant Liability
Class of Warrant or Right [Line Items]
Warrants issued to purchase common stock	6,113	6,113
Warrant Exercise Price	22.50
Expiration Dates	Jun. 01, 2016
Issued in August 2011 financing | Warrant Liability
Class of Warrant or Right [Line Items]
Warrants issued to purchase common stock	565,759	565,759
Warrant Exercise Price	18.75
Expiration Dates	Aug. 01, 2016
Issued to placement agents in August 2011 financing | Warrant Liability
Class of Warrant or Right [Line Items]
Warrants issued to purchase common stock	50,123	50,123
Warrant Exercise Price	13.635
Expiration Dates	Aug. 01, 2016
Issued in Series B, D and E Preferred Stock offerings | Warrant Liability
Class of Warrant or Right [Line Items]
Warrants issued to purchase common stock	76,120	76,120
Warrant Exercise Price	2.50
Issued with Convertible Notes | Warrant Liability
Class of Warrant or Right [Line Items]
Warrants issued to purchase common stock	1,125,578	1,125,578
Warrant Exercise Price	2.50
Expiration Dates	Jun. 01, 2018
Issued in Series E Preferred Stock offering
Class of Warrant or Right [Line Items]
Warrant Exercise Price			7.50	7.50	7.50	7.50	7.50	7.50
Issued in Series E Preferred Stock offering | Warrant Liability
Class of Warrant or Right [Line Items]
Warrants issued to purchase common stock	1,568,823	1,568,823
Warrant Exercise Price	7.50
Expiration Dates	Dec. 01, 2018