Premiums and Reinsurance Related Information - Premiums and Reinsurance, Allowance For Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	$ 21,524	$ 19,823
Cumulative effect adjustment resulting from changes in accounting principles	21,524	19,823
Provision for expected credit losses	582	1,013
Allowance for expected credit losses at June 30, 2020	22,106	22,106
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020	6,800	690
Cumulative effect adjustment resulting from changes in accounting principles	7,175	7,175
Reinsurance Recoverable, Credit Loss Expense (Reversal)	375	558
Allowance for expected credit losses at June 30, 2020	$ 7,175	7,175
Cumulative effect adjustment resulting from changes in accounting principles
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020		1,270
Cumulative effect adjustment resulting from changes in accounting principles		1,270
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses at January 1, 2020		5,927
Cumulative effect adjustment resulting from changes in accounting principles		$ 5,927