Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net loss	$ (53,430)	$ (40,462)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	490	522
Amortization of premiums (accretion of discounts) on investments	0	(154)
Non-cash lease expense	861	1,008
(Gain) Loss on disposal of property and equipment	(39)	67
Stock-based compensation expense	4,186	3,734
Non-cash interest expense	406	338
Warrant liabilities revaluation	3,606	0
Loss on extinguishment of debt	461	0
Net realized losses on investments	0	(1)
Changes in operating assets and liabilities:
Accounts receivable	(7,626)	0
Prepaid expenses, deposits and other assets	(6,656)	3,070
Accounts payable	(29)	378
Deferred revenue	99,512	(13)
Accrued expenses and other liabilities	389	(7,046)
Net cash provided by (used in) operating activities	42,131	(38,559)
Cash flows from investing activities
Receipts from the maturity of short-term investments	0	16,350
Purchases of short-term investments	0	(18,188)
Sale of short term investments	0	1,992
Purchases of property and equipment	(625)	(10)
Proceeds from the sale of property and equipment	50	94
Net cash (used in) provided by investing activities	(575)	238
Cash flows from financing activities
Proceeds from issuance of long-term debt, net of expenses	24,838	0
Repayments of principal on outstanding debt	(19,313)	(700)
Net proceeds from issuance of common stock	0	30,942
Issuance costs paid for December 2019 financing	(4,381)	0
Other financing fees	(192)	0
Proceeds from exercise of pre-funded and common warrants	978	0
Proceeds from exercise of stock options	101	150
Proceeds from issuance of common stock under Employee Stock Purchase Plan	184	28
Net cash provided by financing activities	14,621	36,507
Effect of exchange rate changes on cash	(88)	24
Net change in cash, cash equivalents, and restricted cash	56,089	(1,790)
Cash, cash equivalents, and restricted cash at beginning of period	91,551	37,682
Cash, cash equivalents, and restricted cash at end of period	147,640	35,892
Supplement cash flow information
Cash paid for interest	519	1,652
Noncash investing and financing activities
Cashless warrant exercise	18,228	0
Reclassification of warrant liability to equity upon exercise of warrants	1,494	0
Fair value of warrants issued in connection with issuance of long-term debt	444	0
Purchase of property and equipment not yet paid	17	0
Equity offering costs in accrued liabilities	117	0
Debt issuance costs in accrued liabilities	100	0
At-The-Market Offering
Cash flows from financing activities
Net proceeds from issuance of common stock	2,137	372
Private Placement
Cash flows from financing activities
Net proceeds from issuance of common stock	$ 10,269	$ 5,715