Consolidated Statement of Changes in Common Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Treasury Stock [Member]	Premium on Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balances at Dec. 31, 2012	$ 1,499,213	$ 60,962	$ (21,072)	$ 416,619	$ 1,075,074	$ (32,370)
Balance (in shares) at Dec. 31, 2012			(606,025)
Balance (in shares) at Dec. 31, 2012		60,961,570
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Common stock issued for compensatory plans	3,074	85	286	2,703
Common stock issued for compensatory plans (in shares)		85,436	8,233
Treasury Stock Acquired [Abstract]
Repurchase of common stock (in shares)	0
Dividends on common stock	(42,614)				(42,614)
Net Income	69,166				69,166
Other comprehensive income, net of tax	2,495					2,495
Balances at Jun. 30, 2013	1,531,334	61,047	(20,786)	419,322	1,101,626	(29,875)
Balance (in shares) at Jun. 30, 2013			(597,792)
Balance (in shares) at Jun. 30, 2013		61,047,006
Balances at Dec. 31, 2013	1,586,197	61,047	(20,601)	422,624	1,149,003	(25,876)
Balance (in shares) at Dec. 31, 2013	(592,486)		(592,486)
Balance (in shares) at Dec. 31, 2013	61,047,006	61,047,006
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Common stock issued for compensatory plans	(7)	4	5,318	(5,329)
Common stock issued for compensatory plans (in shares)		4,280	152,394
Treasury Stock Acquired [Abstract]
Repurchase of common stock	(12,449)		(12,449)
Repurchase of common stock (in shares)			(250,000)
Dividends on common stock	(46,435)				(46,435)
Net Income	62,557				62,557
Other comprehensive income, net of tax	1,388					1,388
Balances at Jun. 30, 2014	$ 1,591,251	$ 61,051	$ (27,732)	$ 417,295	$ 1,165,125	$ (24,488)
Balance (in shares) at Jun. 30, 2014	(690,092)		(690,092)
Balance (in shares) at Jun. 30, 2014	61,051,286	61,051,286