Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Cash flows from operating activities:
Net loss			$ (51,002)	$ (23,293)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	$ 127	$ 91	387	272
Impairment of acquired IPR&D			21,692
Changes in fair value of financial instruments			52	280
Change in fair value of contingent consideration			131	2,108
Noncash interest			83	395
Loss on extinguishment of debt				1,816
Acquired IPR&D			995
Foreign currency gain/(loss)	7	71	(87)	225
Amortization of debt issuance costs			332	301
Accretion on discount to short-term investments and convertible promissory notes			(546)	(34)
Stock-based compensation			2,792	350
Issuance of call option derivative				344
Provision (benefit) for deferred taxes			(4,555)
Changes in operating assets and liabilities:
Grant and award receivable				400
Tax refund receivable			(1,393)	(785)
Prepaid expenses and other current assets			969	(1,272)
Deferred rent			(23)	(14)
Accounts payable and accrued expenses			1,391	143
Net cash used in operating activities			(28,782)	(18,764)
Cash flows from investing activities:
Cash acquired through Merger				3,442
Purchase of property and equipment			(81)	(61)
Purchase of available-for-sale securities			(88,104)	(33,443)
Maturities of available-for-sale securities			64,346
Sale of available-for-sale securities, net			9,351
Net cash used in investing activities			(14,488)	(30,062)
Cash flows from financing activities:
Proceeds from debt facility				14,894
Proceeds from convertible promissory notes				3,569
Issuance of common stock upon exercise of warrants			19	384
Issuance of common stock upon public offering, net			45,792	39,522
Issuance of common stock upon at the market offerings, net			493	991
Repayment of long-term debt				(3,567)
Proceeds from exercise of stock options			50
Capital lease obligation principal payments			(257)	(460)
Net cash provided by financing activities			46,097	55,333
Effect of exchange rate changes on cash and cash equivalents			(2)	(67)
Increase in cash and cash equivalents			2,825	6,440
Cash and cash equivalents beginning of period			22,121	13,373	$ 13,373
Cash and cash equivalents end of period	$ 24,946	$ 19,813	24,946	19,813	$ 22,121
Non-cash transactions:
Extinguishment and derecognition of put options				2,202
Shares issued in connection of business combination and assumed equity awards				35,846
Accretion of redeemable convertible preferred stock				578
Beneficial conversion feature				404
Common stock issued for IPR&D, net			995
Supplemental disclosure of cash flow information:
Cash paid for interest			$ 1,038	359
Common Stock [Member]
Non-cash transactions:
Conversion of convertible notes into common stock				$ 8,249