Condensed Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Operating activities
Net (loss) income	$ (7,028)	$ 2,705
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
Non-cash compensation expense	809	51
Change in fair value of liability under license agreement		(35)
Accrued interest and amortization of beneficial conversion feature on promissory notes		2,604
Depreciation and amortization	393	395
Deferred rent costs	(130)	(117)
Amortization of financing costs		78
Changes in operating assets and liabilities:
Other receivables	(480)	(31)
Income tax receivable	4	(27)
Prepaid expenses and other current assets	(561)	(22)
Accounts payable and accrued expenses	69	339
Deferred revenue	(406)	5,394
Net cash (used in) provided by operating activities	(7,330)	11,334
Investing activities
Purchases of property and equipment	(6)
Net cash (used in) investing activities	(6)
Financing activities
Proceeds from convertible promissory notes		1,462
Financing costs on convertible promissory notes		(70)
Repayment of long-term debt		(307)
Proceeds from sale of Junior A convertible preferred stock, net		7,642
Proceeds from initial public offering, net of issuance costs	57,762
Proceeds from the exercise of stock options	29
Net cash provided by financing activities	57,791	8,727
Net cash increase for the period	50,455	20,061
Cash and cash equivalents at beginning of period	12,357	1,117
Cash and cash equivalents at end of period	62,812	21,178
Supplemental disclosure of cash flow information
Cash paid for interest		24
Noncash financing activities
Conversion of convertible preferred stock to common stock	65,586
Reclassification of prepaid IPO costs paid in 2013	1,465
Unpaid IPO issuance costs	$ 50