Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities:
Net loss	$ (28,856)	$ (28,874)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	309	269
Stock-based compensation	2,460	2,422
Amortization of debt discount and issuance costs	268	113
Changes in operating assets and liabilities:
Accounts receivable	1,910	(3,483)
Grants and other receivables	0	118
Prepaid expenses and other assets	425	(1,342)
Inventory	(2,225)	1,419
Accounts payable	2,131	584
Accrued expenses and other liabilities	(4,390)	(920)
Cash used in operating activities	(27,968)	(29,694)
Investing activities:
Purchases of property and equipment	(70)	(168)
Cash used in investing activities	(70)	(168)
Financing activities:
Proceeds from long-term debt	30,000	0
Cash paid for financing costs	(622)	0
Proceeds from issuance of common stock under employee stock purchase plan	0	173
Proceeds from the exercise of stock options	0	15
Cash provided by financing activities	29,378	188
Effects of exchange rate changes on cash and cash equivalents	(5)	(6)
Net decrease in cash, cash equivalents and restricted cash	1,335	(29,680)
Cash, cash equivalents and restricted cash at beginning of period	147,165	201,011
Cash, cash equivalents and restricted cash at end of period	148,500	171,331
Supplemental disclosure of noncash activities:
Fixed asset purchases within accounts payable and accrued expenses	218	146
Recognition of right-of-use assets	405	2,484
Recognition of lease liabilities	$ 405	$ 2,961