Consolidated Statement of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Flows from Operating Activities
Net loss	$ (91,148,000)	$ (39,209,000)	$ (17,014,000)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	2,003,000	634,000	240,000
Amortization of intangibles	549,000	89,000	0
Accretion of discounts and amortization of premiums on marketable securities	1,831,000	725,000
Stock-based compensation	15,006,000	8,430,000	570,000
Excess tax benefit from stock-based compensation	(4,444,000)
Loss from remeasurement of fair value of contingent consideration	400,000
Loss from remeasurement of fair value of warrants		26,077,000	566,000
Gain from changes in the fair value of preferred stock derivative liability			(1,475,000)
Gain on extinguishment of convertible promissory notes			(3,553,000)
Non-cash interest expense related to convertible promissory notes payable			2,380,000
Loss on disposal of property and equipment	15,000
Deferred income tax	(7,800,000)
Changes in operating assets and liabilities:
Accounts receivable	3,708,000	(1,693,000)	(2,796,000)
Prepaid expenses and other assets	3,487,000	(2,654,000)	(1,117,000)
Accounts payable	(2,851,000)	1,537,000	1,681,000
Deferred revenue	(15,068,000)	157,064,000	35,962,000
Accrued clinical trial and manufacturing expenses	(745,000)	2,172,000	2,460,000
Accrued expenses and other liabilities	8,981,000	1,638,000	1,461,000
Net cash (used in) provided by operating activities	(86,076,000)	154,810,000	19,365,000
Cash Flows from Investing Activities
Purchase of marketable securities	(359,500,000)	(359,378,000)
Proceeds from maturities of marketable securities	351,322,000	77,885,000
Restricted cash	(468,000)
Purchase of property and equipment	(23,887,000)	(2,174,000)	(782,000)
Acquisition, net of cash acquired		(14,321,000)
Net cash used in investing activities	(32,533,000)	(297,988,000)	(782,000)
Cash Flows from Financing Activities
Proceeds from issuance of common stock, net of offering costs	36,806,000	150,283,000
Excess tax benefit from stock-based compensation	4,444,000
Deferred offering costs			(1,092,000)
Proceeds from issuance of convertible promissory note payable to related parties			308,000
Repayment of note payable to related party			(200,000)
Proceeds from issuance of convertible preferred stock, net of issuance costs		22,522,000	93,276,000
Proceeds from exercise of stock options and warrants	1,000,000	801,000	49,000
Proceeds from employee stock purchase plan	835,000	572,000
Net cash provided by financing activities	43,085,000	174,178,000	92,341,000
Net (decrease) increase in cash and cash equivalents	(75,524,000)	31,000,000	110,924,000
Cash and cash equivalents at beginning of period	150,456,000	119,456,000	8,532,000
Cash and cash equivalents at end of period	74,932,000	150,456,000	119,456,000
Supplemental Disclosure
Cash paid for interest			18,000
Cash paid for taxes	22,400,000
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Stock issued in connection with business acquisition		11,452,000
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	$ 447,000	$ 692,000
Series C Convertible Preferred Stock
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Issuance of convertible preferred stock in connection with conversion of convertible promissory notes			13,452,000
Series B Convertible Preferred Stock
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Issuance of convertible preferred stock in connection with conversion of convertible promissory notes			$ 4,956,000