Marketable securities (Detail) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Amortized cost / Cost
Marketable securities	$ 8,949,000	$ 70,494,000
Unrealized gains
Marketable securities	0	0
Unrealized losses
Marketable securities	(3,000)	(1,759,000)
Fair value
Marketable securities	8,946,000	68,735,000
Debt securities, available-for-sale, noncurrent	0	0
U.S. government agency securities and treasuries
Amortized cost / Cost
Debt securities	8,949,000	67,970,000
Unrealized gains
Debt securities	0	0
Unrealized losses
Debt securities	(3,000)	(1,733,000)
Fair value
Debt securities	$ 8,946,000	66,237,000
Corporate bonds
Amortized cost / Cost
Debt securities		2,524,000
Unrealized gains
Debt securities		0
Unrealized losses
Debt securities		(26,000)
Fair value
Debt securities		$ 2,498,000