Allowance for Expected Credit Losses - Ceded credit risk (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Concentration Risk [Line Items]
Reinsurance recoverable for paid and unpaid claims and claims adjustments		$ 6,563,654	$ 5,880,735	$ 4,500,802
Shareholders' equity | Reinsurer concentration risk | Largest balance due from any one carrier
Concentration Risk [Line Items]
Concentration risk percentage		9.00%	6.70%
AM Best "A-" Or Better Rating | Reinsurance recoverable | Reinsurer concentration risk
Concentration Risk [Line Items]
Concentration risk percentage		68.80%	69.70%
Rating Below A- | Reinsurance recoverable | Reinsurer concentration risk | All Other Carriers
Concentration Risk [Line Items]
Concentration risk percentage		0.10%	0.10%
No AM Best rating | Reinsurance recoverable | Reinsurer concentration risk | Reinsurance trusts or letters of credit
Concentration Risk [Line Items]
Concentration risk percentage		95.00%	91.00%
No AM Best rating | Reinsurance recoverable | Reinsurer concentration risk | All Other Carriers
Concentration Risk [Line Items]
Concentration risk percentage	[1]	31.10%	30.20%

[1] At December 31, 2022 and 2021 period, over 95% and 91% of such amount is collateralized through reinsurance trusts, funds withheld arrangements, letters of credit or other, respectively