Investments in debt and equity securities - Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Gains	$ 2,635	$ 678
Losses	23,693	35,472
Municipal
Debt Securities, Available-for-sale [Line Items]
Gains	0	3
Losses	170	272
Corporate
Debt Securities, Available-for-sale [Line Items]
Gains	764	489
Losses	11,946	18,535
Foreign
Debt Securities, Available-for-sale [Line Items]
Gains	1,765	165
Losses	11,097	16,212
U.S. Treasury Bonds
Debt Securities, Available-for-sale [Line Items]
Gains	106	21
Losses	$ 480	$ 453