Condensed Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Operating activities
Net loss	$ (17,112)	$ (11,160)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	53	49
Amortization of debt discount and beneficial conversion feature		459
Amortization of debt issuance costs		18
Amortization of premiums and discounts on investments	106
Revaluation of warrants	0	2,587
Noncash interest expense on convertible notes		459
Stock-based compensation expense	1,676	153
Loss related to assets held for sale	29	29
(Gain)/Loss on sale of assets	1	(5)
Changes in assets and liabilities:
Prepaids and other assets	(992)	214
Accounts payable	1,789	288
Other accrued liabilities	(732)	1,103
Net cash used in operating activities	(15,182)	(5,806)
Investing activities
Purchases of investments	(4,800)
Proceeds from sales/maturities of investments	6,926
Proceeds from sale of assets	12	56
Purchase of property and equipment	(638)	(18)
Net cash provided by investing activities	1,500	38
Financing activities
Payments for offering costs in connection with initial public offering		(1,067)
Proceeds from issuance of preferred stock, net of issuance costs		16,827
Proceeds from exercise of common stock options	142	123
Proceeds from warrant issuance	78
Proceeds from debt issuance, net of issuance costs	4,869
Net cash provided by financing activities	5,089	15,883
Net increase (decrease) in cash and cash equivalents	(8,593)	10,115
Cash and cash equivalents at beginning of period	56,537	6,512
Cash and cash equivalents at end of period	47,944	16,627
Supplemental disclosure of cash flow information:
Deferred offering costs not yet paid		1,383
Convertible promissory note
Supplemental disclosure of cash flow information:
Conversion of promissory notes, including accrued interest into Series A - 1 preferred stock		16,623
Pfizer note
Supplemental disclosure of cash flow information:
Conversion of promissory notes, including accrued interest into Series A - 1 preferred stock		$ 7,803