Consolidated Statements of Changes in Common Shareholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Premium on Common Stock [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss [Member]
Shareholders' equity, balance at Dec. 31, 2009	$ 1,115,043	$ 60,277	$ 399,148	$ 667,220	$ (311)	$ (11,291)
Shareholders' equity, balance (in shares) at Dec. 31, 2009		(60,277,462)			(18,094)
Common stock issued for compensatory plans	6,392	263	6,129	0
Common stock issued for compensatory plans (in shares)		262,162
Issuance of treasury stock	73		36		37
Issuance of treasury stock (in shares)					4,596
Dividend requirements, preferred stock, net	(46)			(46)
Dividends on common stock	(59,328)			(59,328)
Net income	255,391			255,391
Other comprehensive loss, net of tax	(347)					(347)
Shareholders' equity, balance at Dec. 31, 2010	1,317,178	60,540	405,313	863,237	(274)	(11,638)
Shareholders' equity, balance (in shares) at Dec. 31, 2010		(60,539,624)			(13,498)
Common stock issued for compensatory plans	4,685	162	4,523	0
Common stock issued for compensatory plans (in shares)		162,718
Issuance of treasury stock	136		68		68
Issuance of treasury stock (in shares)					3,095
Repurchase of treasury stock	(13,009)				(13,009)
Repurchase of treasury stock (in shares)					(400,000)
Dividend requirements, preferred stock, net	(26)			(26)
Stock redemption costs, preferred stock, net	(112)			(112)
Dividends on common stock	(68,342)			(68,342)
Net income	195,848			195,848
Other comprehensive loss, net of tax	(16,501)					(16,501)
Shareholders' equity, balance at Dec. 31, 2011	1,419,857	60,702	409,904	990,605	(13,215)	(28,139)
Shareholders' equity, balance (in shares) at Dec. 31, 2011		(60,702,342)			(410,403)
Common stock issued for compensatory plans	6,961	260	6,701	0
Common stock issued for compensatory plans (in shares)		259,228
Issuance of treasury stock	164		14		150
Issuance of treasury stock (in shares)					4,378
Repurchase of treasury stock	(8,007)				(8,007)
Repurchase of treasury stock (in shares)					(200,000)
Dividends on common stock	(79,179)			(79,179)
Net income	163,648			163,648
Other comprehensive loss, net of tax	(4,231)					(4,231)
Shareholders' equity, balance at Dec. 31, 2012	$ 1,499,213	$ 60,962	$ 416,619	$ 1,075,074	$ (21,072)	$ (32,370)
Shareholders' equity, balance (in shares) at Dec. 31, 2012		(60,961,570)			(606,025)