Schedule II - Financial Information of Registrant - Parent Company Balance Sheet (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investments
Fixed-maturities available for sale—at fair value (amortized cost of $747,309 and $485,727)	$ 5,017,711	$ 5,517,078
Equity securities—at fair value (cost of $140,733)	148,965	184,245
Other invested assets—at fair value	5,511	4,165
Short-term investments—at fair value (includes $61,328 and $1,058 of reinvested cash collateral held under securities lending agreements)	402,090	551,508
Total investments	5,693,491	6,513,542
Cash	56,183	151,145
Investment in subsidiaries, at equity in net assets (Note C)	4,300,000
Accounts and notes receivable (Note C)	119,834	124,016
Other assets (Note C)	427,024	483,180
Total assets	7,063,729	7,839,185
Liabilities
Senior notes	1,413,504	1,409,473
Net deferred tax liability (Note A)	391,083	337,509
Other liabilities (Note C)	333,604	296,614
Total liabilities	3,144,402	3,580,389
Common stockholders’ equity
Common stock ($0.001 par value; 485,000 shares authorized; 2022: 176,509 and 157,056 shares issued and outstanding, respectively; 2021: 194,408 and 175,421 shares issued and outstanding, respectively)	176	194
Treasury stock, at cost (2022: 19,453 shares; 2021: 18,987 shares)	(930,643)	(920,798)
Additional paid-in capital	1,519,641	1,878,372
Retained earnings	3,786,952	3,180,935
Accumulated other comprehensive income (loss)	(456,799)	120,093
Total common stockholders’ equity	3,919,327	4,258,796	$ 4,284,353
Total liabilities and stockholders’ equity	7,063,729	7,839,185
Balance Sheet Parentheticals [Abstract]
Fixed-maturities available for sale, amortized cost	5,587,261	5,367,729
Equity securities, amortized cost	162,899	176,229
Reinvested cash collateral held under securities lending agreements	$ 99,735	$ 48,652
Common stock, par value (in usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	485,000	485,000
Common stock, shares, issued (in shares)	176,509	194,408
Common stock, shares, outstanding (in shares)	157,056	175,421	191,606	201,164
Treasury stock (in shares)	19,453	18,987
Parent Company
Investments
Fixed-maturities available for sale—at fair value (amortized cost of $747,309 and $485,727)	$ 675,948	$ 481,659
Equity securities—at fair value (cost of $140,733)	140,804	0
Other invested assets—at fair value	3,958	3,511
Short-term investments—at fair value (includes $61,328 and $1,058 of reinvested cash collateral held under securities lending agreements)	108,232	120,601
Total investments	928,942	605,771
Cash	1,872	38,846
Investment in subsidiaries, at equity in net assets (Note C)	4,576,644	5,210,917
Accounts and notes receivable (Note C)	657	100,002
Other assets (Note C)	157,370	65,923
Total assets	5,665,485	6,021,459
Liabilities
Senior notes	1,413,504	1,409,473
Net deferred tax liability (Note A)	196,829	283,585
Other liabilities (Note C)	135,825	69,605
Total liabilities	1,746,158	1,762,663
Common stockholders’ equity
Common stock ($0.001 par value; 485,000 shares authorized; 2022: 176,509 and 157,056 shares issued and outstanding, respectively; 2021: 194,408 and 175,421 shares issued and outstanding, respectively)	176	194
Treasury stock, at cost (2022: 19,453 shares; 2021: 18,987 shares)	(930,643)	(920,798)
Additional paid-in capital	1,519,641	1,878,372
Retained earnings	3,786,952	3,180,935
Accumulated other comprehensive income (loss)	(456,799)	120,093
Total common stockholders’ equity	3,919,327	4,258,796
Total liabilities and stockholders’ equity	5,665,485	6,021,459
Balance Sheet Parentheticals [Abstract]
Fixed-maturities available for sale, amortized cost	747,309	485,727
Equity securities, amortized cost	140,733
Reinvested cash collateral held under securities lending agreements	$ 61,328	$ 1,058