Fair value measurements - Schedule of Changes in Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Corporate equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 1,190		$ 0
Total realized and unrealized gain (losses)	(20)		0
Purchases and issuances	0		1,170
Sales and settlements	0		0
Transfers in (out)	0		0
Ending balance	1,170		1,170
Corporate debt and other obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,862		0
Total realized and unrealized gain (losses)	111		143
Purchases and issuances	0		1,830
Sales and settlements	0		0
Transfers in (out)	0		0
Ending balance	1,973		1,973
Auction rate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	128	$ 2,713	2,652	$ 2,713
Total realized and unrealized gain (losses)	0	3	206	3
Purchases and issuances	0	0	0	0
Sales and settlements	0	(35)	(2,730)	(35)
Transfers in (out)	0	0	0	0
Ending balance	128	$ 2,681	128	$ 2,681
Trade claims
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance			2,684
Total realized and unrealized gain (losses)			957
Purchases and issuances			534
Sales and settlements			(4,175)
Transfers in (out)			0
Ending balance	$ 0		$ 0