CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (85,462)	$ (18,753)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	3,088	1,886
Depreciation expense	17	4
Non-cash interest expense		280
Change in fair value of warrant liability	1,182	454
Change in fair value of derivative liability		(289)
Change in fair value of contingent equity liability		3,375
Loss from equity method investment	728	218
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(5,270)	(480)
Accounts payable	4,224	2,656
Accrued expenses	(27)	2,991
Other long-term liabilities	(13)	6
Net cash used in operating activities	(81,533)	(7,652)
Cash flows from investing activities:
Purchases of property and equipment	(357)	(21)
Purchase of equity method investment	(1,375)	(1,624)
Net cash used in investing activities	(1,732)	(1,645)
Cash flows from financing activities:
Proceeds from issuance of common shares	55,000
Proceeds from issuance of Series A preferred shares		40,000
Payments of offering costs		(2,049)
Proceeds from exercise of stock options	1,003
Net cash provided by financing activities	56,003	37,951
Net increase (decrease) in cash	(27,262)	28,654
Cash at beginning of period	131,468	23,692
Cash at end of period	104,206	52,346
Supplemental disclosure of cash flow information:
Cash paid for interest		25
Cash paid for income taxes	80
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs included in accounts payable and accrued expenses	$ 2,987	1,515
Deferred Series A offering costs included in accrued expenses		65
Beneficial conversion feature on Series A preferred shares		12,006
Accretion of beneficial conversion feature on Series A preferred shares		4,000
Issuance of Series A preferred shares as payment of offering costs		1,242
Issuance of common shares as payment of equity investment		$ 352