Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net loss	$ (55,154)	$ (16,283)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	172	66
Stock-based compensation	4,123	1,029
Amortization of debt discount and issuance costs	180	194
Loss on sale of equipment	1	0
Changes in operating assets and liabilities:
Accounts receivable	(3,671)	0
Grants and other receivables	(165)	165
Prepaid expenses and other assets	(859)	1,893
Inventory	(2,723)	0
Accounts payable	2,917	(1,683)
Accrued expenses and other liabilities	7,686	985
Cash used in operating activities	(47,493)	(13,634)
Investing activities:
Purchases of property and equipment	(881)	(711)
Cash used in investing activities	(881)	(711)
Financing activities:
Proceeds from the sale of Series D preferred stock	0	36,712
Proceeds from the sale of common stock	63,969	0
Cash paid for financing costs	(6,349)	(278)
Proceeds from the exercise of stock options	857	0
Cash provided by financing activities	58,477	36,434
Effects of exchange rate changes on cash and cash equivalents	25	(6)
Net increase in cash, cash equivalents and restricted cash	10,128	22,083
Cash, cash equivalents and restricted cash at beginning of period	234,875	36,847
Cash, cash equivalents and restricted cash at end of period	245,003	58,930
Supplemental disclosure of noncash financing activities:
Deemed dividend	0	7,150
Accretion to redemption value	0	1,074
Fixed asset purchases within accounts payable and accrued expenses	233	0
Fixed asset additions acquired through tenant allowance	267	0
Financing costs within accounts payable and accrued expenses	188	1,507
Conversion of convertible notes payable and accrued interest into Series C-2 preferred stock	$ 0	$ 19,527