Allowance for Expected Credit Losses - Premiums receivable (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Credit Loss [Abstract]
Balance at beginning of period		$ 3,634,182	$ 2,866,578	$ 2,633,280	$ 2,064,586
Balance at end of period		3,579,380	2,807,720	3,579,380	2,807,720
Allowance for Expected Credit Losses
Balance at beginning of period		38,170	35,979	39,958	37,781
Change for provision of expected credit losses	[1]	59	2,736	(1,729)	934
Balance at end of period		38,229	38,715	38,229	38,715
Premium receivable, write-offs during the period		$ 1,900	$ 1,200	$ 6,600	$ 2,400

[1] Amounts deemed uncollectible are written-off in operating expenses. For the 2022 third quarter and 2021 third quarter, amounts written off were $1.9 million and $1.2 million, respectively. For the nine months ended September 30, 2022 and 2021 period, amounts written off were $6.6 million and $2.4 million, respectively.