CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock Member	Additional Paid In Capital Member	Retained Earnings Member	Treasury Stock Member	Accumulated Other Comprehensive Income Member
Total stockholders equity at Dec. 31, 2015	$ 6,135,381	$ 791	$ 1,816,142	$ 4,620,303	$ (1,010,139)	$ 708,284
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	701,443			701,443
Other Comprehensive Income (Loss), Net of Tax	431,045					431,045
Dividends to stockholders, $2.20 per share	(100,371)			(100,371)
Purchase of treasury stock	(122,916)				122,916
Reissuance of treasury stock	(48,500)		(32,469)	(22,245)	(38,276)
Total stockholders equity at Dec. 31, 2016	7,093,082	791	1,848,611	5,199,130	(1,094,779)	1,139,329
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	156,400
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Accounting Standards Update 2018 02 [Member]	17,723			(138,649)		156,372
Net Income (Loss) Attributable to Parent	1,822,181			1,822,181
Other Comprehensive Income (Loss), Net of Tax	767,930					767,930
Dividends to stockholders, $2.20 per share	(117,291)			(117,291)
Purchase of treasury stock	(43,508)				43,508
Reissuance of treasury stock	(29,418)		(22,295)	(29,106)	(36,229)
Total stockholders equity at Dec. 31, 2017	9,569,535	791	1,870,906	6,736,265	(1,102,058)	2,063,631
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	2,600
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Accounting Standards Update 2018 02 [Member]	(2,020)			553		(2,573)
Net Income (Loss) Attributable to Parent	715,842			715,842
Other Comprehensive Income (Loss), Net of Tax	(1,424,295)					(1,424,295)
Dividends to stockholders, $2.20 per share	(140,110)			(140,110)
Purchase of treasury stock	(299,679)				299,679
Reissuance of treasury stock	(31,280)		(27,746)	(27,601)	(31,135)
Total stockholders equity at Dec. 31, 2018	$ 8,450,553	$ 791	$ 1,898,652	$ 7,284,949	$ (1,370,602)	$ 636,763