Fair value measurements - Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Auction rate securities - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets Beginning Balance	$ 31,682	$ 31,977	$ 31,776	$ 31,804
Total Realized and Unrealized Gain (Losses)	3,153	(29)	3,159	(56)
Purchases and Issuances	0	1,175	0	1,375
Sales and Settlements	(32,122)	0	(32,222)	0
Transfers In (Out)	0	0	0	0
Assets Ending Balance	$ 2,713	$ 33,123	$ 2,713	$ 33,123