CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (100,108)	$ (38,065)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	10,805	2,167
Depreciation expense	21	2
Non-cash interest expense	784	93
Fair value of warrants issued as consideration for license agreement		2,127
Change in fair value of warrant liability	5,509	(2)
Change in fair value of derivative liability	(512)	105
Change in fair value of contingent equity liability	13,082	13,125
Loss from equity method investment	1,204	75
Non-cash amortization of fair value of warrant issued as consideration for service	29
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,282)	(484)
Deferred tax assets	9
Accounts payable	7,978	982
Accrued expenses	10,371	6,426
Other long-term liabilities	62
Net cash used in operating activities	(54,048)	(13,449)
Cash flows from investing activities:
Purchases of property and equipment	(253)	(5)
Purchase of equity method investment	(2,999)	(3,000)
Decrease in restricted cash	127
Net cash used in investing activities	(3,125)	(3,005)
Cash flows from financing activities:
Proceeds from issuance of common shares		11,399
Proceeds from issuance of common shares upon completion of initial public offering, net of underwriting commissions and discounts	179,996
Proceeds from issuance of Series A preferred shares	40,000
Payments of related party notes payable	(595)
Proceeds from borrowings		5,000
Repayment of notes payable	(5,000)
Payments of offering costs	(5,039)	(238)
Net cash provided by financing activities	209,362	16,161
Net increase in cash	152,189	(293)
Cash at beginning of period	23,565	1,460
Cash at end of period	175,754	1,167
Supplemental disclosure of cash flow information:
Cash paid for interest	122
Cash paid for income taxes	450
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs included in accounts payable and accrued expenses	29	71
Debt issuance costs included in accrued expenses		26
Issuance of warrants to guarantor and co-guarantor of notes payable		$ 934
Beneficial conversion feature on Series A preferred shares	12,006
Accretion of beneficial conversion feature on Series A preferred shares	12,006
Issuance of Series A preferred shares as payment of offering costs	1,242
Issuance of common shares as payment of equity investment	352
Issuance of common share warrant as consideration for services	93
Exercise of stock options	255
Purchases of property and equipment included in accounts payable	$ 9