Schedule II. Condensed Financial Information of Registrant (Condensed Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Assets:
Short-term investments	$ 81,740				$ 114,121
Total investments	19,724,043				18,208,368
Cash	103,156				92,559
Other receivables	630,223				589,171
Other assets	832,413				819,630
Total assets	28,051,499	$ 26,223,345	$ 26,769,793	$ 26,922,329	25,986,797	$ 25,248,899	$ 26,424,294	$ 28,215,723
Liabilities:
Short-term debt	486,113				449,103
Long-term debt	1,629,559				1,627,952
Other liabilities	487,632				542,223
Total liabilities	23,564,696	$ 21,600,214	$ 22,789,487	$ 23,076,038	22,037,220	$ 21,638,930	$ 23,203,991	$ 25,671,448
Shareholders' equity:
Preferred stock	0				0
Common stock	102,218				105,218
Additional paid-in-capital	532,474				529,661
Accumulated other comprehensive income	(2,772,419)				(2,790,313)
Retained earnings	7,478,813				6,894,535
Total shareholders' equity	4,486,803				3,949,577				$ 2,003,808	$ 933,521	$ 8,771,092
Total liabilities and shareholders' equity	28,051,499				25,986,797
Parent Company
Assets:
Long-term investments	42,360				31,651
Short-term investments	1,005				15,001
Total investments	43,365				46,652
Cash	1,003				58
Investment in affiliates	6,539,183				5,940,586
Taxes receivable from affiliates	14,163				14,161
Other assets	181,443				173,044
Total assets	6,884,436				6,305,854
Liabilities:
Short-term debt	486,113				449,103
Long-term debt	1,779,137				1,777,490
Other liabilities	132,383				129,684
Total liabilities	2,397,633				2,356,277
Shareholders' equity:
Preferred stock	351				351
Common stock	102,218				105,218
Additional paid-in-capital	882,985				880,172
Accumulated other comprehensive income	(2,772,419)				(2,790,313)
Retained earnings	7,478,813				6,894,535
Treasury stock	(1,205,145)				(1,140,386)
Total shareholders' equity	4,486,803				3,949,577
Total liabilities and shareholders' equity	6,884,436				6,305,854
Parent Company | Related Party
Assets:
Other receivables	$ 105,279				$ 131,353