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		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Corporate equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 0		$ 0
Total realized and unrealized gain (losses)	20		20
Purchases and issuances	1,170		1,170
Sales and settlements	0		0
Transfers in (out)	0		0
Ending balance	1,190		1,190
Corporate debt and other obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0		0
Total realized and unrealized gain (losses)	32		32
Purchases and issuances	1,830		1,830
Sales and settlements	0		0
Transfers in (out)	0		0
Ending balance	1,862		1,862
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	0	206	0
Purchases and issuances	0	0	0	0
Sales and settlements	0	0	(2,730)	0
Transfers in (out)	0	0	0	0
Ending balance	128	$ 2,713	128	$ 2,713
Trade claims
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	3,218		2,684
Total realized and unrealized gain (losses)	957		957
Purchases and issuances	0		534
Sales and settlements	(4,175)		(4,175)
Transfers in (out)	0		0
Ending balance	$ 0		$ 0