Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Equity [Member]	Common Stock [Member]	Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Beginning balance at Dec. 31, 2012	$ 2,936,399	$ 63,272	$ 1,750	$ 1,602,136	$ 1,281,811	$ 48,603	$ (61,173)
Common stock shares outstanding, beginning balance (in shares) at Dec. 31, 2012			175,013
Preferred stock shares outstanding, beginning balance (in shares) at Dec. 31, 2012		65
Comprehensive income:
Net income	188,692	$ 0	$ 0	0	188,692	0	0
Other comprehensive loss	(72,847)	$ 0	$ 0	0	0	(72,847)	0
Comprehensive income	115,845
Common stock issued:
Stock-based compensation plans, net (in shares)		0	0
Stock-based compensation plans, net	9,305	$ 0	$ 0	989	(17,630)	0	25,946
Purchase of treasury stock	(123,349)	0	0	0	0	0	(123,349)
Cash dividends:
Common stock dividends	(54,991)	0	0	0	(54,991)	0	0
Preferred stock dividends	(5,158)	$ 0	$ 0	0	(5,158)	0	0
Purchase of preferred stock (in shares)		(1)	0
Purchase of preferred stock	1,626	$ 1,410	$ 0	0	216	0	0
Stock-based compensation expense, net	14,840	0	0	14,840	0	0	0
Tax impact of stock-based compensation	25	0	0	25	0	0	0
Ending balance at Dec. 31, 2013	2,891,290	$ 61,862	$ 1,750	1,617,990	1,392,508	(24,244)	(158,576)
Common stock shares outstanding, ending balance (in shares) at Dec. 31, 2013			175,013
Preferred stock shares outstanding, ending balance (in shares) at Dec. 31, 2013		64
Comprehensive income:
Net income	190,509	$ 0	$ 0	0	190,509	0	0
Other comprehensive loss	19,394	$ 0	$ 0	0	0	19,394	0
Comprehensive income	209,903
Common stock issued:
Stock-based compensation plans, net (in shares)		0	0
Stock-based compensation plans, net	13,228	$ 0	$ 0	2,553	(21,171)	0	31,846
Purchase of treasury stock	(112,312)	0	0	0	0	0	(112,312)
Cash dividends:
Common stock dividends	(58,710)	0	0	0	(58,710)	0	0
Preferred stock dividends	(5,002)	$ 0	$ 0	0	(5,002)	0	0
Purchase of preferred stock (in shares)		(2)	0
Purchase of preferred stock	2,451	$ 2,135	$ 0	0	316	0	0
Stock-based compensation expense, net	16,091	0	0	16,091	0	0	0
Tax impact of stock-based compensation	(1,288)	$ 0	$ 0	(1,288)	0	0	0
Purchase of common stock returned to authorized but unissued (in shares)		0	(8,469)
Purchase of common stock returned to authorized but unissued	(150,498)	$ 0	$ (85)	(150,413)	0	0	0
Ending balance at Dec. 31, 2014	2,800,251	$ 59,727	$ 1,665	1,484,933	1,497,818	(4,850)	(239,042)
Common stock shares outstanding, ending balance (in shares) at Dec. 31, 2014			166,544
Preferred stock shares outstanding, ending balance (in shares) at Dec. 31, 2014		62
Comprehensive income:
Net income	188,301	$ 0	$ 0	0	188,301	0	0
Other comprehensive loss	(27,766)	$ 0	$ 0	0	0	(27,766)	0
Comprehensive income	160,535
Common stock issued:
Stock-based compensation plans, net (in shares)		0	0
Stock-based compensation plans, net	20,054	$ 0	$ 0	3,316	(22,538)	0	39,276
Acquisition of Ahmann & Martin Co. (in shares)		0	2,621
Acquisition of Ahmann & Martin Co.	43,530	$ 0	$ 26	43,504	0	0	0
Purchase of treasury stock	(5,154)	0	0	0	0	0	(5,154)
Cash dividends:
Common stock dividends	(62,400)	0	0	0	(62,400)	0	0
Preferred stock dividends	(7,155)	$ 0	$ 0	0	(7,155)	0	0
Purchase of preferred stock (in shares)		(2)	0
Purchase of preferred stock	1,335	$ 1,209	$ 0	0	126	0	0
Other (in shares)		0	0
Stock-based compensation expense, net	18,202	$ 0	$ 0	18,202	0	0	0
Tax impact of stock-based compensation	1,518	$ 0	$ 0	1,518	0	0	0
Purchase of common stock returned to authorized but unissued (in shares)		0	(4,965)
Purchase of common stock returned to authorized but unissued	(93,000)	$ 0	$ (49)	(92,951)	0	0	0
Issuance of preferred stock (in shares)		(65)	0
Issuance of preferred stock	62,966	$ 62,966	$ 0	0	0	0	0
Other	(766)	(105)	0	0	(661)	0	0
Ending balance at Dec. 31, 2015	$ 2,937,246	$ 121,379	$ 1,642	$ 1,458,522	$ 1,593,239	$ (32,616)	$ (204,920)
Common stock shares outstanding, ending balance (in shares) at Dec. 31, 2015			164,200
Preferred stock shares outstanding, ending balance (in shares) at Dec. 31, 2015		125