Investments in debt and equity securities - Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Gains	$ 1,400	$ 2,635
Losses	25,149	23,693
Municipal
Debt Securities, Available-for-sale [Line Items]
Gains	2	0
Losses	228	170
Corporate
Debt Securities, Available-for-sale [Line Items]
Gains	515	764
Losses	12,420	11,946
Foreign
Debt Securities, Available-for-sale [Line Items]
Gains	858	1,765
Losses	11,757	11,097
U.S. Treasury Bonds
Debt Securities, Available-for-sale [Line Items]
Gains	25	106
Losses	$ 744	$ 480