Statement of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended			84 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Operating Activities
Net loss	$ (51,145)	$ (14,562)	$ (18,633)	$ (151,775)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	20	31	32	174
Amortization of debt issuance costs	88	47		135
Accretion of debt discount	87	59		146
Non-cash change in fair value of warrant liability	1,181	366	7	1,563
Non-cash change in fair value of investor rights liability				(683)
Loss on extinguishment of debt	1,091			1,091
Share-based compensation	2,871	640	248	4,061
Series A-1, Series B-1 and Junior Preferred Stock issued for acquired technology and licenses			500	9,500
Accrued interest expense converted to Series A Preferred Stock				2
Changes in operating assets and liabilities:
Prepaid expense and other current assets	(6,761)	21	135	(6,804)
Other receivables		1,036	(738)
Security deposits	(96)			(255)
Accrued clinical drug supplies and trial costs	1,472	(485)	(822)	2,485
Accounts payable and accrued expenses	2,375	(235)	172	3,754
Deferred rent	42	(22)	(24)	42
Net cash used in operating activities	(48,775)	(13,104)	(19,123)	(136,564)
Investing Activities
Purchase of marketable securities				(4,238)
Maturities of marketable securities			3,400	4,250
Purchase of property, equipment	(5)		(4)	(201)
Net cash used in investing activities	(5)		3,396	(189)
Financing Activities
Payment of debt issuance costs	(43)	(377)		(421)
Proceeds from issuance of common stock	94	2	4	218
Proceeds from initial public offering, net	175,555			175,555
(Repayments on) Proceeds from issuance of notes payable, net	(11,900)	11,387		(302)
Proceeds from issuance of preferred stock, net	49,699		14,990	130,632
Proceeds from royalty purchase agreement	41,667			41,667
Net cash provided by financing activities	255,072	11,012	14,994	347,349
Net change in cash and cash equivalents	206,292	(2,092)	(733)	210,596
Cash and cash equivalents
Beginning of period	4,304	6,396	7,129
End of period	210,596	4,304	6,396	210,596
Supplemental disclosure of cash paid
Interest	1,523	437		1,964
Income Taxes	0
Supplemental disclosures of cash flow information
Conversion of preferred stock to common stock upon completion of IPO	174,310			174,310
Accreted dividends on Series A, Series A-1, Series of B, B-1 and Series C Preferred Stock	5,891	7,063	6,838	33,046
Notes payable and accrued interest converted to Series A Preferred Stock				$ 212