Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			$ 77,259	$ 205,176
Net income	$ 151,770	$ 94,265	232,382	138,938
Other comprehensive loss	16,141	13,982	(46,350)	15,205
Cash dividends
Common			(75,627)	(75,974)
Dividends paid - Preference stock	(10)	(11)	(21)	(22)
Issuance of common stock			(7,346)	(2,023)
Conversion to common stock				0
Stock-based compensation expense			11,067	7,976
Purchase of subsidiary shares from noncontrolling interest				(7,520)
Balances, end of period	191,364	281,756	191,364	281,756
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			(26)	(28)
Balances, end of period	522	563	522	563
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			(34,005)	(24,212)
Conversion to common stock			(543)	(656)
Stock-based compensation expense			11,067	7,976
Purchase of subsidiary shares from noncontrolling interest				(7,520)
Balances, end of period	155,371	172,565	155,371	172,565
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			4,897,708	4,715,564
Net income			232,382	138,938
Cash dividends
Common			(75,627)	(75,974)
Dividends paid - Preference stock			(21)	(22)
Balances, end of period	5,054,442	4,778,506	5,054,442	4,778,506
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balances, beginning of period			(846,156)	(574,556)
Other comprehensive loss			(46,350)	15,205
Cash dividends
Balances, end of period	(892,506)	(559,351)	(892,506)	(559,351)
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			26,659	22,189
Conversion to common stock			569	687
Balances, end of period	$ (4,449,804)	$ (4,433,866)	$ (4,449,804)	$ (4,433,866)