Schedule II Financial Information of Registrant - Parent Company Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Assets
Fixed-maturities available for sale—at fair value (amortized cost of $485,727 and $836,191)	$ 5,517,078	$ 5,723,340
Short-term investments—at fair value	551,508	618,004
Other invested assets—at fair value	4,165	4,973
Total investments	6,513,542	6,788,442
Cash	151,145	87,915
Investment in subsidiaries, at equity in net assets (Note C)	4,800,000
Accounts and notes receivable	124,016	121,294
Other assets (Note C)	837,303	715,085
Total assets	7,839,185	7,948,021
Liabilities and Stockholders’ Equity
Senior notes	1,409,473	1,405,674
Net deferred tax liability (Note A)	337,509	213,897
Other liabilities	296,614	291,855
Total liabilities	3,580,389	3,663,668
Common stock: par value $0.001 per share; 485,000 shares authorized at December 31, 2021 and 2020; 194,408 and 210,130 shares issued at December 31, 2021 and 2020, respectively; 175,421 and 191,606 shares outstanding at December 31, 2021 and 2020, respectively	194	210
Treasury stock, at cost: 18,987 and 18,524 shares at December 31, 2021 and 2020, respectively	(920,798)	(910,115)
Additional paid-in capital	1,878,372	2,245,897
Retained earnings	3,180,935	2,684,636
Accumulated other comprehensive income (loss)	120,093	263,725
Total common stockholders’ equity	4,258,796	4,284,353	$ 4,048,723
Total liabilities and stockholders’ equity	7,839,185	7,948,021
Balance Sheet Parentheticals [Abstract]
Debt Securities, Available-for-sale, Amortized Cost	5,367,729	5,393,623
Equity securities, amortized cost	176,229	145,501
Parent Company
Assets
Fixed-maturities available for sale—at fair value (amortized cost of $485,727 and $836,191)	481,659	844,393
Short-term investments—at fair value	120,601	233,569
Other invested assets—at fair value	3,511	3,000
Total investments	605,771	1,080,962
Cash	38,846	20,141
Investment in subsidiaries, at equity in net assets (Note C)	5,210,917	4,545,508
Accounts and notes receivable	100,002	300,656
Other assets (Note C)	65,923	75,305
Total assets	6,021,459	6,022,572
Liabilities and Stockholders’ Equity
Senior notes	1,409,473	1,405,674
Net deferred tax liability (Note A)	283,585	272,868
Other liabilities	69,605	59,677
Total liabilities	1,762,663	1,738,219
Common stock: par value $0.001 per share; 485,000 shares authorized at December 31, 2021 and 2020; 194,408 and 210,130 shares issued at December 31, 2021 and 2020, respectively; 175,421 and 191,606 shares outstanding at December 31, 2021 and 2020, respectively	194	210
Treasury stock, at cost: 18,987 and 18,524 shares at December 31, 2021 and 2020, respectively	(920,798)	(910,115)
Additional paid-in capital	1,878,372	2,245,897
Retained earnings	3,180,935	2,684,636
Accumulated other comprehensive income (loss)	120,093	263,725
Total common stockholders’ equity	4,258,796	4,284,353
Total liabilities and stockholders’ equity	6,021,459	6,022,572
Balance Sheet Parentheticals [Abstract]
Debt Securities, Available-for-sale, Amortized Cost	$ 485,727	$ 836,191