Income Taxes - Deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Federal net operating loss carryforwards	$ 43,953	$ 37,277
State net operating loss carryforwards	11,433	9,267
Capitalized research and development expenditures	24,485	14,469
Research and development credit carryforwards	10,359	7,104
Lease liability	2,510	2,761
Accruals and reserves	210	241
Intangible assets	1,793	1,917
Stock-based compensation	1,213	1,374
Total deferred tax assets:	95,956	74,410
Valuation allowance	(92,978)	(71,003)
Subtotal	2,978	3,407
Deferred tax liabilities:
Property and equipment	(1,578)	(1,881)
Right of use asset	(1,400)	(1,526)
Total deferred tax liabilities	(2,978)	(3,407)
Total net deferred tax assets