Schedule II - Condensed Financial Information of Registrant (Statements of Income (Parent Company)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Income Statements, Captions [Line Items]
Net investment gains (losses)	$ 103,000	$ 120,703	$ 154,488
Other income	2,596	3,370	681
Total revenues	8,098,925	7,902,196	7,691,651
Operating costs and expense	7,394,123	7,049,276	6,879,557
Income before income taxes	704,802	852,920	812,094
Federal income taxes:
Net federal income tax expense	(171,817)	(168,935)	(163,028)
Net income to common stockholders	530,670	681,944	640,749
Dividends from subsidiaries	617,424	416,027	639,477
Parent Company
Condensed Income Statements, Captions [Line Items]
Management fees and investment income including dividends from subsidiaries of $617,424, $416,027, and $639,477 for the years ended December 31, 2020, 2019 and 2018, respectively	654,485	470,773	697,687
Net investment gains (losses)	3,580	850	(1,685)
Other income	568	117	530
Total revenues	658,633	471,740	696,532
Operating costs and expense	166,892	204,812	191,873
Interest expense	145,417	148,282	155,082
Income before income taxes	346,324	118,646	349,577
Federal income taxes:
Federal income taxes provided by subsidiaries on a separate return basis	188,490	207,647	409,439
Federal income tax expense on a consolidated return basis	(139,679)	(141,190)	(113,138)
Net federal income tax expense	48,811	66,457	296,301
Income before undistributed equity in net income of subsidiaries	395,135	185,103	645,878
Equity in undistributed net income (loss) of subsidiaries	135,535	496,841	(5,129)
Net income to common stockholders	$ 530,670	$ 681,944	$ 640,749