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		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Assets
Assets Beginning Balance	$ 31,776	$ 31,804	$ 31,776	$ 31,804
Total Realized and Unrealized Losses	6	(27)	6	(27)
Purchases and Issuances	0	200	0	200
Sales and Settlements	(100)	0	(100)	0
Transfers In (Out)	0	0	0	0
Assets Ending Balance	$ 31,682	$ 31,977	$ 31,682	$ 31,977