Fair value measurements - Narrative (Detail) - USD ($)	1 Months Ended		3 Months Ended
	Apr. 30, 2022	Jan. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain (loss) on available-for-sale securities			$ 0	$ 0
Interest receivable			300,000		$ 300,000
Interest receivable, write-offs			0	0
Investment at fair value			1,182,000		$ 3,691,000
Proceeds from sale of equity securities		$ 31,300,000
Subsequent Event
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain (loss) on available-for-sale securities	$ 400,000
Debt securities	$ 29,700,000
Other (Expense) Income, Net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on equity securities			$ 2,500,000	$ (28,400,000)