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, 2008	$ 1,059,836	$ 60,066	$ 394,517	$ 615,514	$ (428)	$ (9,833)
Shareholders' equity, balance (in shares) at Dec. 31, 2008		(60,066,345)			(23,831)
Common stock issued for compensatory plans	4,826	211	4,615	0
Common stock issued for compensatory plans (in shares)		211,117
Issuance of treasury stock	133		16		117
Issuance of treasury stock (in shares)					5,737
Dividend requirements, preferred stock, net	(46)			(46)
Dividends on common stock	(54,555)			(54,555)
Net income	106,307			106,307
Other comprehensive loss, net of tax	(1,458)					(1,458)
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)