Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			$ 178,721	$ 77,259
Net income	$ 65,512	$ 89,282	177,148	321,664
Other comprehensive income	14,465	(8,346)	62,673	(54,696)
Dividends paid			(105,791)	(113,158)
Issuance of common stock			(1,321)	(3,963)
Conversion to common stock			0	0
Stock-based compensation expense			16,289	14,921
Repurchase of common stock		(100,000)	(197,267)
Balances, end of period	130,452	142,027	130,452	142,027
Preferred stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			1	1
Conversion to common stock				0
Balances, end of period	1	1	1	1
Preference stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			505	548
Conversion to common stock			(16)	(29)
Balances, end of period	489	519	489	519
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			323,338	323,338
Balances, end of period	323,338	323,338	323,338	323,338
Additional paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			161,280	178,852
Issuance of common stock			(27,251)	(36,946)
Conversion to common stock			(321)	(632)
Stock-based compensation expense			16,289	14,921
Balances, end of period	149,997	156,195	149,997	156,195
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			5,155,537	4,897,708
Net income			177,148	321,664
Dividends paid			(105,791)	(113,158)
Balances, end of period	5,226,894	5,106,214	5,226,894	5,106,214
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			(888,635)	(846,156)
Other comprehensive income			62,673	(54,696)
Balances, end of period	(825,962)	(900,852)	(825,962)	(900,852)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			(4,573,305)	(4,477,032)
Issuance of common stock			25,930	32,983
Conversion to common stock			337	661
Repurchase of common stock		(100,000)	(197,267)
Balances, end of period	$ (4,744,305)	$ (4,543,388)	$ (4,744,305)	$ (4,543,388)