CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net income (loss)	$ 9,733	$ (6,155)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Depreciation and amortization	751	563
Stock-based compensation	1,008	383
Changes in operating assets and liabilities:
Prepaid expenses and other assets	606	(897)
Accounts payable	402	455
Accrued liabilities	(812)	(565)
Deferred rent	96	(7)
Deferred revenue	(22,378)	(857)
Net cash used in operating activities	(10,594)	(7,080)
Cash flows from investing activities:
Maturities of marketable securities	30,349
Purchase of marketable securities	(23,531)
Purchase of property and equipment	(1,445)	(935)
Net cash provided by (used in) investing activities	5,373	(935)
Cash flows from financing activities:
Proceeds from issuances of common stock	37	4
Proceeds from the term loan		4,649
Deferred financing costs		(1,574)
Payments of the term loan	(277)	(109)
Net cash used in (provided by) financing activities	(240)	2,970
Net decrease in cash, cash equivalents and restricted cash	(5,461)	(5,045)
Cash, cash equivalents and restricted cash—beginning of period	39,130	135,633
Cash, cash equivalents and restricted cash—end of period	33,669	130,588
Supplemental disclosures of cash flow information:
Cash paid for interest	35	23
Supplemental disclosures of noncash investing and financing activities:
Purchase of property and equipment included in accrued liabilities	$ 156	75
Deferred financing costs included in accrued liabilities		$ 290