Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Reinsurance Recoverables
Reinsurance recoverable on paid losses	$ 201,194		$ 201,194			$ 282,500
Reinsurance recoverable on unpaid losses	1,086,468		1,086,468			1,111,808
Reinsurance recoverable, allowance for expected credit losses	810		810		$ 517	0
Reinsurance recoverable, net	1,286,852		1,286,852		$ 1,292,636	1,394,308
Reinsurance Liabilities
Unpaid Loss and LAE reserves, assumed	43,707	$ 92,573	43,707	$ 92,573		50,884
Unearned premiums, assumed	18,264		18,264			15,278
Prepaid reinsurance premiums	458,960		458,960			$ 575,747
Premiums:
Direct, Written	1,457,135	1,417,792	4,240,217	4,200,571
Assumed, Written	15,992	17,365	51,065	58,272
Gross premium written	1,473,127	1,435,157	4,291,282	4,258,843
Ceded premiums	(207,871)	(400,553)	(801,515)	(1,064,177)
Net premium written	1,265,256	1,034,604	3,489,767	3,194,666
Direct, Earned	1,429,247	1,407,731	4,189,569	4,080,131
Assumed, Earned	16,318	19,029	48,078	59,872
Premiums Earned, Gross	1,445,565	1,426,760	4,237,647	4,140,003
Ceded, Earned	(266,992)	(373,122)	(918,301)	(1,091,557)
Net earned premium	1,178,573	1,053,638	3,319,346	3,048,446
Loss and LAE expense:
Assumed Loss and LAE	5,888	7,024	19,659	23,670
Ceded Loss and LAE	$ 192,884	$ 245,095	$ 579,535	$ 605,126