Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities:
Net loss	$ (54,708)	$ (56,251)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	563	592
Stock-based compensation	5,232	5,117
Amortization of debt discount and issuance costs	570	234
Changes in operating assets and liabilities:
Accounts receivable	(453)	(7,001)
Grants and other receivables	0	(48)
Prepaid expenses and other assets	1,244	1,096
Inventory	(2,620)	2,803
Accounts payable	253	(4,253)
Accrued expenses and other liabilities	(1,599)	129
Cash used in operating activities	(51,518)	(57,582)
Investing activities:
Purchases of property and equipment	(309)	(423)
Cash used in investing activities	(309)	(423)
Financing activities:
Proceeds from long-term debt	34,447	0
Repayment of long-term debt	(4,447)	0
Cash paid for financing costs	(637)	0
Proceeds from issuance of common stock under employee stock purchase plan	516	612
Proceeds from the exercise of stock options	71	369
Cash provided by financing activities	29,950	981
Effects of exchange rate changes on cash and cash equivalents	(9)	(9)
Net decrease in cash, cash equivalents and restricted cash	(21,886)	(57,033)
Cash, cash equivalents and restricted cash at beginning of period	147,165	201,011
Cash, cash equivalents and restricted cash at end of period	125,279	143,978
Supplemental disclosure of noncash activities:
Fixed asset purchases within accounts payable and accrued expenses	82	35
Recognition of right-of-use assets	742	3,724
Recognition of lease liabilities	$ 742	$ 4,201