Consolidated Statements of Changes in Common Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Premium on Common Stock [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss [Member]
Stockholders' Equity, Beginning Balance at Dec. 31, 2010	$ 1,317,178	$ 60,540	$ 405,313	$ 863,237	$ (274)	$ (11,638)
Treasury stock, Beginning Balance (shares) at Dec. 31, 2010					(13,498)
Common stock issued, Beginning Balance (shares) at Dec. 31, 2010		60,539,624
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Common stock issued for compensatory plans, Value	4,821	162	4,591		68
Common stock issued for compensatory plans (in shares)		162,718			3,095
Treasury Stock Acquired [Abstract]
Repurchase of common stock, Value	(13,009)				(13,009)
Repurchase of common 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 income (loss), net of tax	(16,501)					(16,501)
Stockholders' Equity, Ending Balance at Dec. 31, 2011	1,419,857	60,702	409,904	990,605	(13,215)	(28,139)
Treasury stock, Ending Balance (shares) at Dec. 31, 2011					(410,403)
Common stock issued, Ending Balance (shares) at Dec. 31, 2011		60,702,342
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Common stock issued for compensatory plans, Value	7,125	260	6,715		150
Common stock issued for compensatory plans (in shares)		259,228			4,378
Treasury Stock Acquired [Abstract]
Repurchase of common stock, Value	(8,007)				(8,007)
Repurchase of common stock (in shares)					(200,000)
Dividends on common stock	(79,179)			(79,179)
Net income	163,648			163,648
Other comprehensive income (loss), net of tax	(4,231)					(4,231)
Stockholders' Equity, Ending Balance at Dec. 31, 2012	1,499,213	60,962	416,619	1,075,074	(21,072)	(32,370)
Treasury stock, Ending Balance (shares) at Dec. 31, 2012	(606,025)				(606,025)
Common stock issued, Ending Balance (shares) at Dec. 31, 2012	60,961,570	60,961,570
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Common stock issued for compensatory plans, Value	6,561	85	6,005		471
Common stock issued for compensatory plans (in shares)		85,436			13,539
Treasury Stock Acquired [Abstract]
Dividends on common stock	(86,756)			(86,756)
Net income	160,685			160,685
Other comprehensive income (loss), net of tax	6,494					6,494
Stockholders' Equity, Ending Balance at Dec. 31, 2013	$ 1,586,197	$ 61,047	$ 422,624	$ 1,149,003	$ (20,601)	$ (25,876)
Treasury stock, Ending Balance (shares) at Dec. 31, 2013	(592,486)				(592,486)
Common stock issued, Ending Balance (shares) at Dec. 31, 2013	61,047,006	61,047,006