Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities:
Net (loss) income	$ (29,351)	$ 28,201
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
Depreciation and amortization	104	56
Stock-based compensation	1,800	539
Amortization of debt discount and issuance costs	194	582
Changes in operating assets and liabilities:
Grants and other receivables	159	(333)
Deposits and other assets	2,519	(1,667)
Inventory	(241)	0
Accounts payable	(574)	(524)
Accrued expenses	2,633	(1,207)
Accrued interest	668	2,050
Deferred other income	217	(41)
Cash (used in) provided by operating activities	(21,872)	27,656
Investing activities:
Purchases of property and equipment	(1,210)	(43)
Cash used in investing activities	(1,210)	(43)
Financing activities:
Proceeds from the sale of Series D preferred stock	36,494	0
Cash paid for financing costs	(781)	0
Cash provided by financing activities	35,713	0
Effects of exchange rate changes on cash and cash equivalents	(18)	46
Net increase in cash and cash equivalents	12,613	27,659
Cash and cash equivalents at beginning of period	36,797	15,198
Cash and cash equivalents at end of period	49,410	42,857
Supplemental disclosure of noncash financing activities:
Deferred offering costs within accounts payable and accrued expenses	1,504	0
Conversion of convertible notes payable and accrued interest into Series C-2 preferred stock	19,527	0
Redeemable Convertible Preferred Stock, Series C, C1, C2, and D
Supplemental disclosure of noncash financing activities:
Deemed dividend	11,255	8,254
Redeemable Convertible Preferred Stock, Series C, C1, D
Supplemental disclosure of noncash financing activities:
Deemed dividend	$ 1,093	$ 1,582