Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities:
Net loss	$ (80,277)	$ (29,351)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	325	104
Stock-based compensation	6,325	1,800
Amortization of debt discount and issuance costs	291	194
Loss on sale of equipment	1	0
Changes in operating assets and liabilities:
Accounts receivable	(2,923)	0
Grants and other receivables	(136)	159
Prepaid expenses and other assets	(380)	2,513
Inventory	(4,686)	(241)
Accounts payable	2,566	(574)
Accrued expenses and other liabilities	7,271	3,518
Cash used in operating activities	(71,623)	(21,878)
Investing activities:
Purchases of property and equipment	(1,450)	(1,210)
Cash used in investing activities	(1,450)	(1,210)
Financing activities:
Proceeds from the sale of Series D preferred stock	0	36,494
Proceeds from the sale of common stock	63,969	0
Cash paid for financing costs	(6,464)	(781)
Proceeds from issuance of common stock under employee stock purchase plan	739	0
Proceeds from the exercise of stock options	1,418	0
Cash provided by financing activities	59,662	35,713
Effects of exchange rate changes on cash and cash equivalents	41	(18)
Net increase in cash, cash equivalents and restricted cash	(13,370)	12,607
Cash, cash equivalents and restricted cash at beginning of period	234,875	36,847
Cash, cash equivalents and restricted cash at end of period	221,505	49,454
Supplemental disclosure of noncash financing activities:
Deemed dividend	0	11,255
Accretion to redemption value	0	1,093
Fixed asset purchases within accounts payable and accrued expenses	172	0
Fixed asset additions acquired through tenant allowance	361	0
Financing costs within accounts payable and accrued expenses	82	1,504
Conversion of convertible notes payable and accrued interest into Series C-2 preferred stock	$ 0	$ 19,527