Investments in debt and equity securities - Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Gains	$ 739	$ 678
Losses	34,059	35,472
Municipal
Debt Securities, Available-for-sale [Line Items]
Gains	1	3
Losses	325	272
Corporate
Debt Securities, Available-for-sale [Line Items]
Gains	433	489
Losses	17,121	18,535
Foreign
Debt Securities, Available-for-sale [Line Items]
Gains	293	165
Losses	15,876	16,212
U.S. Treasury Bonds
Debt Securities, Available-for-sale [Line Items]
Gains	12	21
Losses	$ 737	$ 453