Condensed Consolidated Statement of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash Flows from Operating Activities
Net loss	$ (61,582,000)	$ (42,309,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,230,000	381,000
Amortization of intangible assets	415,000	0
Accretion of discounts and amortization of premiums on marketable securities	1,462,000	165,000
Stock-based compensation	10,852,000	5,232,000
Excess tax benefit from stock-based compensation	(4,921,000)
Gain from remeasurement of fair value of contingent consideration	(313,000)
Loss from remeasurement of fair value of warrants		26,077,000
Changes in operating assets and liabilities:
Accounts receivable	3,790,000	6,000
Prepaid expenses and other assets	(2,939,000)	(2,455,000)
Accounts payable	(3,346,000)	2,209,000
Deferred revenue	(11,253,000)	165,195,000
Accrued clinical trial and manufacturing expenses	1,761,000	1,536,000
Accrued expenses and other liabilities	4,294,000	1,717,000
Net cash (used in) provided by operating activities	(60,550,000)	157,754,000
Cash Flows from Investing Activities
Purchase of marketable securities	(316,098,000)	(267,513,000)
Proceeds from maturities of marketable securities	306,264,000
Restricted cash	(468,000)
Purchase of property and equipment	(19,479,000)	(1,816,000)
Net cash used in investing activities	(29,781,000)	(269,329,000)
Cash Flows from Financing Activities
Proceeds from issuance of common stock, net of offering costs	31,849,000	150,283,000
Proceeds from issuance of convertible preferred stock, net of issuance costs		22,522,000
Excess tax benefit from stock-based compensation	4,921,000
Proceeds from exercise of stock options and warrants	574,000	305,000
Proceeds from employee stock purchase plan	514,000
Net cash provided by financing activities	37,858,000	173,110,000
Net (decrease) increase in cash and cash equivalents	(52,473,000)	61,535,000
Cash and cash equivalents at beginning of period	150,456,000	119,456,000
Cash and cash equivalents at end of period	97,983,000	180,991,000
Supplemental Disclosure of Cash Flow Information
Cash paid for taxes	18,900,000
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Conversion of convertible preferred stock to common stock		164,964,000
Reclassification of warrant liabilities to additional paid-in capital		27,066,000
Purchase of property and equipment in accounts payable and accrued liabilities	$ 3,667,000	$ 79,000