Net realized and unrealized gains - Gross Realized and Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Realized gains	$ 1,683	$ 7,909	$ 3,277	$ 8,080
Realized losses	(3,671)	0	(3,839)	(2,469)
Net unrealized investment (losses) gains recognized on equity securities still held at end of period	(9,917)	3,745	(7,258)	9,318
Investment and other gains (losses) – net	$ (11,905)	$ 11,654	$ (7,820)	$ 14,929