Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities:
Net loss		$ (121,359)	$ (83,795)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense		11,827	8,702
Depreciation and amortization expense		3,255	2,902
Non-cash operating lease cost		2,305	1,465
Amortization of premiums on investments		547	1,581
Amortization of debt issuance costs		328	241
Collaboration (profit) loss sharing - related party		(705)	0
Changes in operating assets and liabilities:
Prepaid expenses and other current and other non-current assets		(10,145)	(3,579)
Accounts receivable		0	8,136
Deferred revenue - related party		(2,709)	(9,911)
Accounts payable		709	1,684
Operating lease liabilities		(2,130)	(1,012)
Accrued expenses and other current and long-term liabilities (3)	[1]	1,735	4,395
Net cash used in operating activities		(116,342)	(69,191)
Cash flows from investing activities:
Purchases of property and equipment		(5,113)	(3,896)
Purchases of investments		(36,138)	(51,942)
Sales and maturities of investments		77,622	82,378
Purchase of restricted investments		0	(750)
Net cash provided by investing activities		36,371	25,790
Cash flows from financing activities:
Proceeds from exercise of stock options		387	957
Issuance of common stock under ESPP		892	392
Proceeds from issuance of debt, net of issuance costs		27,606
Repayment of notes payable		(1,907)	0
Net cash provided by financing activities		26,978	1,349
Net decrease in cash, cash equivalents, and restricted cash		(52,993)	(42,052)
Cash, cash equivalents and restricted cash at beginning of period		188,002	116,049
Cash, cash equivalents and restricted cash at end of period		135,009	73,997
Supplemental disclosure of cash flow information:
Cash paid for interest		1,836	1,220
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued expenses		597	606
Prepaid rent reclassified to right-of-use assets		4,962
Lease liability arising from obtaining right-of-use assets		$ 4,370	$ 4,839

[1] Includes related party amounts of $1,379 and $0 at June 30, 2022 and June 30, 2021, respectively (see Note 11)