Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities
Net loss	$ (24,597)	$ (19,620)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	207	231
Amortization of premiums and discounts on marketable securities	14	0
Non-cash lease expense	272	366
Loss on disposal of property and equipment	0	1
Stock-based compensation expense	1,780	1,409
Non-cash interest expense	387	123
Warrant liabilities revaluation	16,747	846
Changes in operating assets and liabilities:
Accounts receivable	(1,118)	5,000
Prepaid expenses, deposits and other assets	(1,512)	(61)
Accounts payable	151	836
Deferred revenue	(2,728)	0
Accrued expenses and other liabilities	(1,736)	(829)
Net cash (used in) operating activities	(12,133)	(11,698)
Cash flows from investing activities
Purchases of marketable securities	(22,420)	0
Purchases of property and equipment	(25)	(135)
Net cash (used in) investing activities	(22,445)	(135)
Cash flows from financing activities
Repayments of principal on outstanding debt	0	(2,100)
Net proceeds from issuance of common stock	20,991	1,141
Issuance costs paid for December 2019 financing	0	(4,381)
Other financing fees	0	(147)
Proceeds from exercise of stock options	244	3
Proceeds from issuance of common stock under Employee Stock Purchase Plan	72	114
Net cash provided by (used in) financing activities	21,307	(5,370)
Effect of exchange rate changes on cash	(7)	(84)
Net change in cash, cash equivalents, and restricted cash	(13,278)	(17,287)
Cash, cash equivalents, and restricted cash at beginning of period	140,064	91,551
Cash, cash equivalents, and restricted cash at end of period	126,786	74,264
Supplement cash flow information
Cash paid for interest	494	232
Noncash investing and financing activities
Purchase of property and equipment not yet paid	10	10
Equity offering costs in accrued liabilities	48	42
Unrealized (losses) on marketable securities	$ (1)	$ 0