General - Effects of Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Premiums Written
Direct	$ 972,900	$ 828,800	$ 1,926,300	$ 1,786,700
Premiums Earned
Ceded	16,000	12,000	31,000	26,000
Net	926,820	811,898	1,842,741	1,734,471
Property and Casualty Lines [Member]
Premiums Written
Direct	963,418	823,031	1,910,024	1,772,775
Ceded	(15,785)	(10,041)	(31,428)	(21,399)
Assumed	218	205	12,887	7,835
Net	947,851	813,195	1,891,483	1,759,211
Premiums Earned
Direct	931,833	814,559	1,852,900	1,741,600
Ceded	(15,617)	(11,818)	(31,160)	(25,563)
Assumed	3,299	2,056	6,590	4,103
Net	$ 919,515	$ 804,797	$ 1,828,330	$ 1,720,140