Schedule II - Condensed Financial Information of Registrant (Balance Sheets (Parent Company)) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Cash and cash equivalents	$ 2,372,366	$ 1,023,710
Fixed maturity securities available for sale at fair value (cost $792,752 and $718,642 at December 31, 2020 and 2019, respectively)	14,159,369	14,180,961
Current federal income taxes	5,893	23,404
Property, furniture and equipment at cost, less accumulated depreciation	405,930	422,091
Other assets	700,215	762,743
Total assets	28,606,913	26,662,144
Liabilities:
Other liabilities	1,178,546	1,244,888
Current federal income taxes	41,282	10,006
Deferred federal income taxes	42,161	26,416
Subordinated debentures	1,102,309	1,198,704
Total liabilities	22,281,116	20,543,802
Stockholders' equity:
Preferred stock	0	0
Common stock	70,535	70,535
Additional paid-in capital	1,012,483	1,056,042
Retained earnings (including accumulated undistributed net income of subsidiaries of $5,700,515 and $5,564,980 at December 31, 2020 and 2019, respectively)	8,348,381	7,932,372
Accumulated other comprehensive loss	(62,172)	(257,299)
Treasury stock, at cost	(3,058,425)	(2,726,711)
Total common stockholders’ equity	6,310,802	6,074,939
Total liabilities and equity	28,606,913	26,662,144
Fixed maturity securities available for sale at cost	13,682,286	13,897,964
Parent Company
Assets:
Cash and cash equivalents	296,960	389,801
Fixed maturity securities available for sale at fair value (cost $792,752 and $718,642 at December 31, 2020 and 2019, respectively)	800,263	723,959
Loans receivable	75,789	55,794
Equity securities, at fair value (cost $3,430 in 2020 and 2019 respectively.)	3,430	3,430
Investment in subsidiaries	7,957,501	7,623,639
Current federal income taxes	0	18,857
Property, furniture and equipment at cost, less accumulated depreciation	11,412	12,323
Other assets	11,231	13,294
Total assets	9,156,586	8,841,097
Liabilities:
Due to subsidiaries	77,860	107,245
Other liabilities	106,064	118,593
Current federal income taxes	15,662	0
Deferred federal income taxes	31,851	22,846
Subordinated debentures	1,102,309	1,198,704
Senior notes	1,512,038	1,318,770
Total liabilities	2,845,784	2,766,158
Stockholders' equity:
Preferred stock	0	0
Common stock	70,535	70,535
Additional paid-in capital	1,012,483	1,056,042
Retained earnings (including accumulated undistributed net income of subsidiaries of $5,700,515 and $5,564,980 at December 31, 2020 and 2019, respectively)	8,348,381	7,932,372
Accumulated other comprehensive loss	(62,172)	(257,299)
Treasury stock, at cost	(3,058,425)	(2,726,711)
Total common stockholders’ equity	6,310,802	6,074,939
Total liabilities and equity	9,156,586	8,841,097
Fixed maturity securities available for sale at cost	792,752	718,642
Equity securities available for sale at cost	3,430	3,430
Accumulated undistributed net income of subsidiaries	$ 5,700,515	$ 5,564,980