Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Stockholders' equity, beginning balance at Dec. 31, 2014	$ 4,697,466	$ 0	$ 134,218	$ 457,613	$ 997,452	$ 3,376,846	$ (268,663)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive income (loss)	(193,375)				(442,133)	248,758
Common dividends declared ($.27 in 2015 and $.28 in 2016)	(34,004)					(34,004)
Acquisition of treasury stock	(211,567)						(211,567)
Stock-based compensation	15,040			8,189		(2,132)	8,983
Exercise of stock options	32,496			10,989		(20,753)	42,260
Stockholders' equity, ending balance at Jun. 30, 2015	4,306,056	0	134,218	476,791	555,319	3,568,715	(428,987)
Stockholders' equity, beginning balance at Mar. 31, 2015					1,165,641
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive income (loss)	(483,212)
Stockholders' equity, ending balance at Jun. 30, 2015	4,306,056	0	134,218	476,791	555,319	3,568,715	(428,987)
Stockholders' equity, beginning balance at Dec. 31, 2015	4,055,552	0	130,218	482,284	231,947	3,614,369	(403,266)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive income (loss)	1,019,672				757,210	262,462
Common dividends declared ($.27 in 2015 and $.28 in 2016)	(33,766)					(33,766)
Acquisition of treasury stock	(202,975)						(202,975)
Stock-based compensation	13,989			7,442		(2,224)	8,771
Exercise of stock options	25,286					(23,175)	48,461
Stockholders' equity, ending balance at Jun. 30, 2016	4,877,758	0	130,218	489,726	989,157	3,817,666	(549,009)
Stockholders' equity, beginning balance at Mar. 31, 2016					535,475
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive income (loss)	592,111
Stockholders' equity, ending balance at Jun. 30, 2016	$ 4,877,758	$ 0	$ 130,218	$ 489,726	$ 989,157	$ 3,817,666	$ (549,009)