Schedule II - Condensed Financial Information of Registrant (Statements of Cash Flows (Parent Company)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net income	$ 1,381,062	$ 1,022,490	$ 530,670
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	55,872	129,682	135,065
Stock incentive plans	49,411	46,680	49,658
Change in:
Other liabilities	19,878	89,467	43,039
Net cash from operating activities	2,568,604	2,183,987	1,616,686
Cash from (used in) investing activities:
Proceeds from sale of fixed maturity securities	797,948	1,842,139	3,832,555
Proceeds from maturities and prepayments of fixed maturity securities	4,891,179	6,067,230	3,864,327
Cost of purchases of fixed maturity securities	(8,036,680)	(10,716,748)	(7,551,591)
Change in loans receivable	(83,212)	(27,421)	1,467
Change in balances due from security brokers	14,337	(17,983)	(26,515)
Net cash (used in) from investing activities	(1,891,355)	(2,989,146)	119,696
Cash (used in) from financing activities:
Purchase of common treasury shares	(94,140)	(122,426)	(346,357)
Cash dividends to common stockholders	(235,192)	(355,736)	(84,147)
Other, net	(12,848)	(45,162)	(56,225)
Net cash (used in) from financing activities	(771,992)	5,831	(397,843)
Net (decrease) increase in cash and cash equivalents	(119,497)	(803,523)	1,348,656
Cash and cash equivalents at beginning of year	1,568,843	2,372,366	1,023,710
Cash and cash equivalents at end of year	1,449,346	1,568,843	2,372,366
Parent Company
Cash flows from operating activities:
Net income	1,381,062	1,022,490	530,670
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	(1,007)	(1,474)	(3,580)
Depreciation and amortization	4,281	18,761	15,133
Equity in undistributed earnings of subsidiaries	(1,511,478)	(763,367)	(135,535)
Tax payments received from subsidiaries	321,682	328,851	165,495
Federal income taxes provided by subsidiaries on a separate return basis	(414,660)	(294,731)	(188,489)
Stock incentive plans	49,411	48,440	49,599
Change in:
Federal income taxes	(40,746)	(22,017)	32,069
Other assets	3,163	(33,319)	1,220
Other liabilities	87,100	(11,758)	3,964
Accrued investment income	890	755	836
Net cash from operating activities	(120,302)	292,631	471,382
Cash from (used in) investing activities:
Proceeds from sale of fixed maturity securities	543,549	402,046	414,802
Proceeds from maturities and prepayments of fixed maturity securities	83,134	654,134	258,413
Cost of purchases of fixed maturity securities	(109,289)	(1,071,823)	(747,713)
Change in loans receivable	(16,249)	(18,227)	(20,023)
Investments in and advances to subsidiaries, net	(171,062)	(1,411)	(100,704)
Change in balances due from security brokers	(10,289)	10,487	(245)
Net additions to real estate, furniture & equipment	(432)	(1,496)	(81)
Other, net	368	95	103
Net cash (used in) from investing activities	319,730	(26,195)	(195,448)
Cash (used in) from financing activities:
Net proceeds from issuance of senior notes	(914)	1,029,579	736,609
Repayment and redemption of debt	(426,503)	(400,000)	(650,000)
Purchase of common treasury shares	(94,140)	(122,426)	(346,357)
Cash dividends to common stockholders	(235,192)	(355,736)	(84,147)
Other, net	(23,194)	(30,776)	(24,880)
Net cash (used in) from financing activities	(779,943)	120,641	(368,775)
Net (decrease) increase in cash and cash equivalents	(580,515)	387,077	(92,841)
Cash and cash equivalents at beginning of year	684,037	296,960	389,801
Cash and cash equivalents at end of year	$ 103,522	$ 684,037	$ 296,960