Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (21,071)	$ (7,152)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	699	196
Loss on disposal of property and equipment	2	7
Equity-based compensation	4,700	845
Benefit from intraperiod tax allocation		(766)
Changes in operating assets and liabilities:
Accounts receivable	(112)
Prepaid expenses and other current assets	(162)	(360)
Accounts payable	154	405
Accrued expenses	1,741	1,220
Deferred revenue	67,260	10,004
Other assets	(2,675)	(841)
Other long-term liabilities	(17)	170
Net cash provided by operating activities	50,519	3,728
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(2,760)	(1,705)
Net cash used in investing activities	(2,760)	(1,705)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from sale of Class A-2 preferred units and Series B preferred stock		74,661
Payments to acquire in-process research and development	(600)	(900)
Payment of preferred unit and preferred stock issuance costs	(100)	(2,622)
Proceeds from common stock offering	170,507
Payment of common stock offering costs	(2,764)	(395)
Net cash provided by financing activities	167,043	70,744
Net increase in cash and cash equivalents	214,802	72,767
Cash and cash equivalents, beginning of period	75,816	9,845
Cash and cash equivalents, end of period	290,618	82,612
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Purchases of property and equipment unpaid at period end	$ 944	144
Acquisition of in-process research and development unpaid at period end		800
Financing costs incurred but unpaid at period end		$ 792