SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets
Fixed income, available-for-sale	$ 5,409,698	$ 6,587,581
Cash and cash equivalents	327,384	284,690
Accrued investment income	55,178	51,902
Total assets	6,213,793	7,325,008
Liabilities:
Senior notes	641,724	881,508
Convertible junior subordinated debentures	21,086	110,204
Other liabilities	154,966	191,702
Total liabilities	1,571,053	2,463,626
Shareholders’ equity:
Common stock (one dollar par value, shares authorized 1,000,000; shares issued 2022 - 371,353; 2021 - 371,353; shares outstanding 2022 - 293,433; 2021 - 320,336)	371,353	371,353
Paid-in capital	1,798,842	1,794,906
Treasury stock at cost (shares 2022 - 77,920; 2021 - 51,017)	(1,050,238)	(675,265)
Accumulated other comprehensive income, net of tax	(481,511)	119,697
Retained earnings	4,004,294	3,250,691
Total shareholders' equity	4,642,740	4,861,382	$ 4,698,986
Total liabilities and shareholders' equity	6,213,793	7,325,008
Parenthetical information [Abstract]
Fixed income, amortized cost	$ 5,926,785	$ 6,397,658
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	371,353,000	371,353,000
Common stock, shares outstanding (in shares)	293,433,000	320,336,000
Treasury stock, shares at cost (in shares)	77,920,000	51,017,000
Revenues:
Investment income, net of expenses	$ 167,476	$ 156,438	154,396
Net gains (losses) on investments and other financial instruments	(7,463)	5,861	12,576
Total revenues	1,172,785	1,185,675	1,199,146
Expenses:
Interest expense	48,054	71,360	59,595
Loss on debt extinguishment	40,199	36,914	26,736
Total losses and expenses	82,751	383,898	639,883
Income before tax	1,090,034	801,777	559,263
Provision for income taxes	224,685	166,794	113,170
Net income	865,349	634,983	446,093
Other comprehensive income (loss), net of tax	(601,208)	(97,124)	144,113
Comprehensive income	264,141	537,859	590,206
Cash flows from operating activities:
Net income	865,349	634,983	446,093
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred federal	(5,235)	4,392	28,244
Loss on debt extinguishment	40,199	36,914	26,736
Change in certain assets and liabilities:
Accrued investment income	(3,276)	(1,905)	(292)
Net cash provided by operating activities	650,012	696,317	732,309
Cash flows from investing activities:
Purchases of investments	(674,406)	(1,531,129)	(2,636,972)
Proceeds from sales of investments	399,661	473,904	836,851
Net cash provided by (used in) investing activities	410,485	(160,749)	(772,506)
Cash flows from financing activities:
Proceeds from issuance of senior notes	0	0	640,250
Payment of original issue discount - senior notes	0	0	(2,969)
Purchase of convertible junior subordinated debentures	(89,118)	(98,610)	(36,392)
Payment of original issue discount- convertible junior subordinated debentures	0	0	(15,049)
Redemption of 5.75% senior notes	(242,296)	0	0
Cash portion of loss on debt extinguishment	(39,514)	(36,914)	(25,266)
Repurchase of common stock	(385,573)	(290,818)	(119,997)
Dividends paid	(110,947)	(94,219)	(82,061)
Payment of debt issuance costs	0	0	(2,020)
Payment of withholding taxes related to share-based compensation net share settlement	(10,094)	(6,729)	(8,940)
Net cash (used in) provided by financing activities	(1,032,542)	(527,290)	167,821
Net increase in cash and cash equivalents and restricted cash and cash equivalents	27,955	8,278	127,624
Cash and cash equivalents and restricted cash and cash equivalents at beginning of year	304,958	296,680	169,056
Cash and cash equivalents and restricted cash and cash equivalents at end of year	332,913	304,958	296,680
Parent Company
Assets
Fixed income, available-for-sale	407,509	538,872
Cash and cash equivalents	239,404	124,164
Investment in subsidiaries, at equity in net assets	4,502,261	4,964,954
Accounts receivable - affiliates	864	2,130
Income taxes - current and deferred	167,966	242,427
Accrued investment income	3,387	2,642
Total assets	5,321,391	5,875,189
Liabilities:
Senior notes	641,724	881,508
Convertible junior subordinated debentures	21,086	110,204
Accrued interest	13,271	20,501
Other liabilities	2,570	1,594
Total liabilities	678,651	1,013,807
Shareholders’ equity:
Common stock (one dollar par value, shares authorized 1,000,000; shares issued 2022 - 371,353; 2021 - 371,353; shares outstanding 2022 - 293,433; 2021 - 320,336)	371,353	371,353
Paid-in capital	1,798,842	1,794,906
Treasury stock at cost (shares 2022 - 77,920; 2021 - 51,017)	(1,050,238)	(675,265)
Accumulated other comprehensive income, net of tax	(481,511)	119,697
Retained earnings	4,004,294	3,250,691
Total shareholders' equity	4,642,740	4,861,382
Total liabilities and shareholders' equity	5,321,391	5,875,189
Parenthetical information [Abstract]
Fixed income, amortized cost	$ 419,751	$ 550,324
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	371,353,000	371,353,000
Common stock, shares outstanding (in shares)	293,433,000	32,336,000
Treasury stock, shares at cost (in shares)	77,920,000	51,017,000
Revenues:
Investment income, net of expenses	$ 7,193	$ 3,850	7,090
Net gains (losses) on investments and other financial instruments	(2,628)	490	1,454
Total revenues	4,565	4,340	8,544
Expenses:
Operating expenses	1,575	1,644	719
Interest expense	47,601	68,359	65,472
Loss on debt extinguishment	38,870	36,914	35,033
Total losses and expenses	88,046	106,917	101,224
Income before tax	(83,481)	(102,577)	(92,680)
Provision for income taxes	(17,851)	(21,240)	(18,431)
Equity in net income of subsidiaries	930,979	716,320	520,342
Net income	865,349	634,983	446,093
Other comprehensive income (loss), net of tax	(601,208)	(97,124)	144,113
Comprehensive income	264,141	537,859	590,206
Cash flows from operating activities:
Net income	865,349	634,983	446,093
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in net income of subsidiaries	(930,979)	(716,320)	(520,342)
Dividends received from subsidiaries	626,695	400,000	221,024
Deferred federal	119,588	(21,551)	(18,252)
Loss on debt extinguishment	38,870	36,914	35,033
Other	33,619	29,799	19,088
Change in certain assets and liabilities:
Accounts receivable - affiliates	1,266	(680)	972
Income taxes receivable	(43,123)	(306)	0
Accrued investment income	931	1,118	(1,262)
Accrued interest	(7,230)	(2,503)	5,076
Net cash provided by operating activities	704,986	361,454	187,430
Cash flows from investing activities:
Purchases of investments	(1,457)	(339,384)	(1,131,060)
Proceeds from sales of investments	287,924	556,384	812,188
Net cash provided by (used in) investing activities	286,467	217,000	(318,872)
Cash flows from financing activities:
Proceeds from issuance of senior notes	0	0	640,250
Purchase of senior notes	0	0	(179,735)
Payment of original issue discount - senior notes	0	0	(2,969)
Purchase of convertible junior subordinated debentures	(89,118)	(98,610)	(36,392)
Payment of original issue discount- convertible junior subordinated debentures	0	0	(15,049)
Redemption of 5.75% senior notes	(242,296)	0	0
Cash portion of loss on debt extinguishment	(38,185)	(36,914)	(25,266)
Repurchase of common stock	(385,573)	(290,818)	(119,997)
Dividends paid	(110,947)	(94,219)	(82,061)
Payment of debt issuance costs	0	0	(2,020)
Payment of withholding taxes related to share-based compensation net share settlement	(10,094)	(6,729)	(8,940)
Net cash (used in) provided by financing activities	(876,213)	(527,290)	167,821
Net increase in cash and cash equivalents and restricted cash and cash equivalents	115,240	51,164	36,379
Cash and cash equivalents and restricted cash and cash equivalents at beginning of year	124,164	73,000	36,621
Cash and cash equivalents and restricted cash and cash equivalents at end of year	$ 239,404	$ 124,164	$ 73,000