Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (43,701)	$ (28,468)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	356	355
Amortization of premiums (accretion of discounts) on investments	0	(131)
Non-cash lease expense	602	723
(Gain) Loss on disposal of property and equipment	(35)	76
Stock‑based compensation expense	2,890	2,431
Non‑cash interest expense	173	267
Warrant liabilities revaluation	8,385	0
Changes in operating assets and liabilities:
Accounts receivable	5,000	0
Prepaid expenses, deposits and other assets	451	2,189
Accounts payable	735	1,363
Deferred revenue	2,000	(11)
Accrued expenses and other liabilities	(362)	(6,231)
Net cash used in operating activities	(23,506)	(27,437)
Cash flows from investing activities
Receipts from the maturity of short-term investments	0	4,850
Purchases of short-term investments	0	(18,188)
Sale of short term investments	0	1,992
Purchases of property and equipment	(334)	(5)
Proceeds from the sale of property and equipment	45	77
Net cash used in investing activities	(289)	(11,274)
Cash flows from financing activities
Repayments of principal on outstanding debt	(4,200)	0
Net proceeds from issuance of common stock	0	30,942
Issuance costs paid for December 2019 financing	(4,381)	0
Other financing fees	(147)	0
Proceeds from exercise of stock options	101	145
Proceeds from issuance of common stock under Employee Stock Purchase Plan	114	20
Net cash (used in) provided by financing activities	(6,327)	31,479
Effect of exchange rate changes on cash	(42)	29
Net change in cash, cash equivalents, and restricted cash	(30,164)	(7,203)
Cash, cash equivalents, and restricted cash at beginning of period	91,551	37,682
Cash, cash equivalents, and restricted cash at end of period	61,387	30,479
Supplement cash flow information
Cash paid for interest	387	634
Noncash investing and financing activities
Cashless warrant exercise	17,089	0
Reclassification of warrant liability to equity upon exercise of warrants	77	0
Purchase of property and equipment not yet paid	111	0
Equity offering costs in accrued liabilities	29	14
Unrealized gain on marketable securities	0	3
At-The-Market Offering
Cash flows from financing activities
Net proceeds from issuance of common stock	2,137	372
Note Warrant
Cash flows from financing activities
Net proceeds from issuance of common stock	$ 49
Proceeds from exercise of pre-funded and common warrants		$ 0