Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net loss	$ (59,203)	$ (11,962)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	750	963
Net amortization of premiums and discounts on investments	(86)	(87)
Stock-based compensation	5,183	3,610
Other non-cash items	110	65
Changes in operating assets and liabilities:
Accounts receivable	0	161
Prepaid expenses and other current assets	(2,460)	1,318
Other assets	(700)	0
Accounts payable	(2,766)	(3,102)
Accrued expenses	2,367	(4,518)
Operating lease assets	1,235	1,290
Operating lease liabilities	(990)	(1,356)
Deferred revenue	(817)	(41,550)
Net cash used in operating activities	(57,377)	(55,168)
Cash flows from investing activities
Maturities of marketable securities	37,500	10,500
Purchase of marketable securities	0	(53,688)
Purchase of property and equipment	(285)	(605)
Net cash provided by (used in) investing activities	37,215	(43,793)
Cash flows from financing activities
Proceeds from exercise of stock options	1,732	121
Proceeds from purchases of common stock under ESPP	333	283
Proceeds from issuance of debt, net of issuance costs	(197)	4,965
Payments under capital lease obligations	(87)	(58)
Net cash provided by financing activities	228,747	97,473
Increase (decrease) in cash, cash equivalents and restricted cash	208,585	(1,488)
Cash, cash equivalents and restricted cash, beginning of period	62,672	60,005
Cash, cash equivalents and restricted cash, end of period	271,257	58,517
Supplemental disclosures of non-cash activities:
Debt financing costs in accrued expenses	0	180
Cash paid for interest	173	64
Right-of-use assets obtained in exchange for operating lease liabilities	9,980	4,778
Right-of-use assets obtained in exchange for financing lease liabilities	0	429
Public Stock Offering
Cash flows from financing activities
Net proceeds from public offering of common stock	163,990	92,162
ATM
Cash flows from financing activities
Net proceeds from public offering of common stock	$ 62,976	$ 0