Premiums and Reinsurance Related Information - Premiums and Reinsurance, Allowance For Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	$ 24,808	$ 22,106	$ 22,883	$ 19,823
Cumulative effect adjustment resulting from changes in accounting principles	23,676	23,033	23,676	23,033
Provision for expected credit losses	(1,132)	927	793	1,940
Allowance for expected credit losses, end of period	23,676	23,033	23,676	23,033
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	7,283	7,175	7,801	690
Cumulative effect adjustment resulting from changes in accounting principles	7,277	7,741	7,277	7,741
Reinsurance Recoverable, Credit Loss Expense (Reversal)	(6)	566	(524)	1,124
Allowance for expected credit losses, end of period	$ 7,277	$ 7,741	7,277	7,741
Cumulative effect adjustment resulting from changes in accounting principles
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period			0	1,270
Cumulative effect adjustment resulting from changes in accounting principles
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period			$ 0	$ 5,927
Cumulative effect adjustment resulting from changes in accounting principles