Condensed Statements of Cash Flows (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Operating activities:
Net loss	$ (26,663,829)	$ (7,219,236)
Adjustments to reconcile net loss to net cash used in operating activities:
Gain on extinguishment of debt and other liabilities		(2,420,000)
Depreciation expense	33,285	26
Amortization of debt issuance costs		4,000
Amortization of premium/discount on investments	124,000	752,000
Stock-based compensation expense	5,123,564	438,052
Changes in operating assets and liabilities:
Accounts receivable	78,000	(80,000)
Prepaid expenses and other current assets	(688,000)	(28,000)
Accounts payable and accrued expenses	3,683,000	2,129,000
Other liabilities	29,000
Net cash used in operating activities	(18,280,000)	(6,424,000)
Investing activities:
Purchase of equipment	(208,000)	(6,000)
Proceeds from maturities of available for sale securities	6,990,000
Purchases of available for sale securities	(64,497,000)	(13,154,000)
Net cash used in investing activities	(57,715,000)	(13,160,000)
Financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs		42,546,000
Repurchase of treasury stock	(79,000)
Proceeds from issuance of common stock, net of issuance costs	104,293,000
Proceeds from receipt of payment on promissory notes issued in exchange for shares of common stock	237,000
Payments on capital lease obligations	(3,000)
Net cash provided by financing activities	104,448,000	42,546,000
Increase in cash and cash equivalents	28,453,000	22,962,000
Cash and cash equivalents at beginning of period	21,215,228	1,641,000
Cash and cash equivalents at end of period	49,667,984	24,603,000
Non-cash financing activities:
Accretion of preferred stock to redemption value	86,899,000	52,862,000
Unpaid initial public offering issuance costs	15,000,000	0
Reclassification of 2012 Series X preferred stock from debt to preferred stock		2,486,000
Conversion of 2012 Series X preferred stock into Series C preferred stock		$ 4,944,000