Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			$ 77,259	$ 205,176
Net income	$ 89,282	$ 132,289	321,664	271,227
Other comprehensive loss	(8,346)	(55,390)	(54,696)	(40,185)
Cash dividends
Common			(113,127)	(113,883)
Dividends paid - Preference stock	(10)	(11)	(31)	(33)
Issuance of common stock			(3,963)	909
Conversion to common stock				0
Stock-based compensation expense			14,921	12,658
Purchase of subsidiary shares from noncontrolling interest				(7,520)
Repurchase of common stock			(100,000)	(50,003)
Balances, end of period	142,027	278,346	142,027	278,346
Preferred stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			1	4
Cash dividends
Conversion to common stock				(3)
Balances, end of period	1	1	1	1
Preference stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			548	591
Cash dividends
Conversion to common stock			(29)	(32)
Balances, end of period	519	559	519	559
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			323,338	323,338
Cash dividends
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			178,852	196,977
Cash dividends
Issuance of common stock			(36,946)	(26,591)
Conversion to common stock			(632)	(741)
Stock-based compensation expense			14,921	12,658
Purchase of subsidiary shares from noncontrolling interest				(7,520)
Balances, end of period	156,195	174,783	156,195	174,783
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			4,897,708	4,715,564
Net income			321,664	271,227
Cash dividends
Common			(113,127)	(113,883)
Dividends paid - Preference stock			(31)	(33)
Balances, end of period	5,106,214	4,872,875	5,106,214	4,872,875
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			(846,156)	(574,556)
Other comprehensive loss			(54,696)	(40,185)
Cash dividends
Balances, end of period	(900,852)	(614,741)	(900,852)	(614,741)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			(4,477,032)	(4,456,742)
Cash dividends
Dividends paid - Preference stock				0
Issuance of common stock			32,983	27,500
Conversion to common stock			661	776
Repurchase of common stock			(100,000)	(50,003)
Balances, end of period	$ (4,543,388)	$ (4,478,469)	$ (4,543,388)	$ (4,478,469)