Investments in debt and equity securities - Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Gains	$ 289	$ 678
Losses	43,036	35,472
Municipal
Debt Securities, Available-for-sale [Line Items]
Gains	1	3
Losses	664	272
Corporate
Debt Securities, Available-for-sale [Line Items]
Gains	136	489
Losses	19,650	18,535
Foreign
Debt Securities, Available-for-sale [Line Items]
Gains	152	165
Losses	21,450	16,212
U.S. Treasury Bonds
Debt Securities, Available-for-sale [Line Items]
Gains	0	21
Losses	$ 1,272	$ 453