Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income (loss)	$ (78,485)	$ 59,337	$ (54,789)
Adjustments to reconcile net loss to net cash provided by (used in) operating    activities:
Depreciation and amortization expense	1,569	1,670	1,785
Stock-based compensation expense	8,546	7,765	5,991
Non-cash interest expense related to note payable	1,069	1,650	74
Net amortization of premiums and discounts on marketable securities	807	(47)	(764)
Loss on disposal of property and equipment	0	1	1
Non-cash operating lease cost	2,041	1,950	1,814
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	1,653	(32)	3,001
Unbilled receivable	518	(2,571)	0
Other assets	74	(431)	12
Accounts payable	(226)	(2,716)	583
Accrued expenses and other current liabilities	2,307	2,436	(710)
Operating lease liability	(2,217)	(423)	(1,778)
Deferred revenue - related party	0	(38,592)	(15,360)
Net cash provided by (used in) operating activities	(62,344)	29,997	(60,140)
Cash flows from investing activities:
Purchases of property and equipment	(120)	(43)	(1,538)
Purchases of marketable securities	(111,632)	(650)	(118,347)
Proceeds from sales or maturities of marketable securities	12,500	59,000	136,850
Net cash provided by (used in) investing activities	(99,252)	58,307	16,965
Cash flows from financing activities:
Proceeds from issuance of convertible note payable, net of issuance costs	10,687	10,000	7,217
Payments of debt issuance costs	0	0	(81)
Proceeds for issuance of common stock, net	29,525	29,086	24
Proceeds from employee stock purchases	266	194	0
Proceeds from exercise of stock options	2,022	802	255
Net cash provided by financing activities	42,500	40,082	7,415
Net increase (decrease) in cash and cash equivalents and restricted cash	(119,096)	128,386	(35,760)
Cash and cash equivalents and restricted cash at beginning of period	176,736	48,350	84,110
Cash and cash equivalents and restricted cash at end of period	57,640	176,736	48,350
Supplemental disclosure of cash flow information:
Cash paid for interest	1,406	1,052	0
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and    accrued expenses	436	1,006	0
Additional right-of-use asset and related lease liability	0	15,003	0
Conversion of note payable into shares of common stock	$ 1,500	$ 2,000	$ 0