Net realized and unrealized gains - Gross Realized and Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Realized gains	$ 183	$ 2,615	$ 3,460	$ 10,695
Realized losses	(65)	(47)	(3,904)	(2,516)
Net unrealized investment (losses) gains recognized on equity securities still held at end of period	(6,492)	319	(13,750)	9,637
Investment and other gains (losses) – net	$ (6,374)	$ 2,887	$ (14,194)	$ 17,816