Income taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
U.S. net operating loss carryforwards (federal and state)	$ 726,021	$ 713,557
Tax credit carryforwards (federal and state)	313,963	300,236
Capitalized license fees and research and development expenses	2,079	1,831
Capitalized research and development expenses under Section 174	91,306	54,885
Stock-based compensation	9,847	11,686
Lease liabilities	100,288	98,296
Accruals and other	20,336	17,325
Total deferred tax assets	1,263,840	1,197,816
Right-of-use assets	(54,976)	(61,388)
Fixed assets	(16,701)	(17,536)
Less valuation allowance	(1,192,163)	(1,118,892)
Net deferred taxes	$ 0	$ 0