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 loss		$ (65,578)	$ (89,127)	$ (70,279)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation expense		20,222	8,824	8,344
Depreciation and amortization expense		5,947	6,578	7,603
Non-cash operating lease cost		3,275	2,315	2,227
Amortization of debt issuance costs		498	446	281
Accretion (amortization) of discount (premium) on issued debt securities		2,526	551	(172)
Loss on disposal of property and equipment				103
Collaboration (profit) loss sharing - related party		(1,732)
Changes in operating assets and liabilities:
Prepaid expenses and other current and non-current assets		(12,337)	(2,186)	3,257
Accounts receivable		9,387	(7,602)	(1,785)
Deferred revenue		(4,357)	(11,565)	(17,520)
Accounts payable		9,362	(1,159)	(1,460)
Operating lease liabilities		(3,550)	(4,456)	(4,211)
Accrued expenses and other liabilities	[1]	43,025	3,771	(2,908)
Net cash provided by (used in) operating activities		6,688	(93,610)	(76,520)
Cash flows from investing activities:
Purchases of property and equipment		(9,566)	(591)	(1,002)
Purchases of investments		(95,971)	(218,284)	(46,420)
Sales and maturities of investments		169,625	59,984	16,904
Net cash provided by (used in) investing activities		64,088	(158,891)	(30,518)
Cash flows from financing activities:
Proceeds from public offering of common stock, net of commissions, underwriting discounts and offering costs			243,748	60,527
Proceeds from Securities Purchase Agreement, net of issuance costs - related party			19,900
Proceeds from issuance of note payable				25,000
Proceeds from at the market equity offering, net of commissions			24,773	512
Payments of debt issuance costs				(425)
Proceeds from exercise of stock options		1,299	14,421	145
Proceeds from issuance of common stock and restricted common stock			120	176
Issuance of common stock under ESPP plan		827	462	296
Repayment of notes payable		(948)
Net cash provided by financing activities		1,178	303,424	86,231
Net increase (decrease) in cash, cash equivalents and restricted cash		71,954	50,923	(20,807)
Effect of exchange rate changes on cash, cash equivalents and restricted cash		(1)
Cash, cash equivalents and restricted cash at beginning of year		116,049	65,126	85,933
Cash, cash equivalents and restricted cash at end of year		188,002	116,049	65,126
Supplemental disclosure of cash flow information:
Cash paid for interest		2,446	2,453	221
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued expenses		874	$ 451	62
Lease liability arising from obtaining right-of-use assets		$ 12,442		$ 154

[1] Includes related party amounts of $31,683 and $0 at December 31, 2021 and December 31, 2020 respectively (see Note 12)