Consolidated Statements of Shareholder's Equity - USD ($) $ in Thousands		Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Beginning balance at Dec. 31, 2013		$ 3,776,342	$ 0	$ 151,218	$ 462,058	$ 210,981	$ 3,495,533	$ (543,448)
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)		1,329,410				786,471	542,939
Common dividends declared ($.51 in 2014, $.54 in 2015 and $.56 in 2016 a share)		(65,998)					(65,998)
Acquisition of treasury stock		(449,308)						(449,308)
Stock-based compensation		32,203			31,315		362	526
Exercise of stock options		74,817			18,524		(22,641)	78,934
Retirement of treasury stock		0		(17,000)	(54,284)		(573,349)	644,633
Ending balance at Dec. 31, 2014		4,697,466	0	134,218	457,613	997,452	3,376,846	(268,663)
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)		(238,405)				(765,505)	527,100
Common dividends declared ($.51 in 2014, $.54 in 2015 and $.56 in 2016 a share)		(67,182)					(67,182)
Acquisition of treasury stock		(418,526)						(418,526)
Stock-based compensation		28,664			21,813		(2,132)	8,983
Exercise of stock options		53,535			17,577		(36,322)	72,280
Retirement of treasury stock		0		(4,000)	(14,719)		(183,941)	202,660
Ending balance at Dec. 31, 2015		4,055,552	0	130,218	482,284	231,947	3,614,369	(403,266)
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)		895,406				345,627	549,779
Common dividends declared ($.51 in 2014, $.54 in 2015 and $.56 in 2016 a share)		(66,968)					(66,968)
Acquisition of treasury stock		(404,784)						(404,784)
Stock-based compensation		26,326			19,659		(2,224)	8,891
Exercise of stock options	[1]	61,329					(53,845)	115,174
Retirement of treasury stock		0		(3,000)	(11,522)		(150,313)	164,835
Ending balance at Dec. 31, 2016		$ 4,566,861	$ 0	$ 127,218	$ 490,421	$ 577,574	$ 3,890,798	$ (519,150)

[1] Certain current year amounts were prospectively adjusted to give effect to the adoption of ASU 2016-09 related to excess tax benefits from stock compensation as described in Note 1—Significant Accounting Policies under "Accounting Pronouncements Adopted in the Current Year."