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]
Stockholders' equity, Beginning Balance at Dec. 31, 2012	$ 1,499,213	$ 60,962	$ (21,072)	$ 416,619	$ 1,075,074	$ (32,370)
Treasury stock, Beginning Balance (in shares) at Dec. 31, 2012			(606,025)
Common stock issued, Beginning 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, Value	1,455	85	110	1,260
Common stock issued for compensatory plans (in shares)		85,436	3,159
Treasury Stock Acquired [Abstract]
Repurchase of common stock (in shares)	0
Dividends on common stock	(20,544)				(20,544)
Net Income	27,133				27,133
Other comprehensive income, net of tax	1,873					1,873
Stockholders' equity, Ending Balance at Mar. 31, 2013	1,509,130	61,047	(20,962)	417,879	1,081,663	(30,497)
Treasury stock, Ending Balance (in shares) at Mar. 31, 2013			(602,866)
Common stock issued, Ending Balance (in shares) at Mar. 31, 2013		61,047,006
Stockholders' equity, Beginning Balance at Dec. 31, 2013	1,586,197	61,047	(20,601)	422,624	1,149,003	(25,876)
Treasury stock, Beginning Balance (in shares) at Dec. 31, 2013	(592,486)		(592,486)
Common stock issued, Beginning 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, Value	(1,661)	4	5,251	(6,916)
Common stock issued for compensatory plans (in shares)		4,280	150,734
Treasury Stock Acquired [Abstract]
Repurchase of common stock, Value	(12,449)		(12,449)
Repurchase of common stock (in shares)	(250,000)		(250,000)
Dividends on common stock	(22,126)				(22,126)
Net Income	25,924				25,924
Other comprehensive income, net of tax	897					897
Stockholders' equity, Ending Balance at Mar. 31, 2014	$ 1,576,782	$ 61,051	$ (27,799)	$ 415,708	$ 1,152,801	$ (24,979)
Treasury stock, Ending Balance (in shares) at Mar. 31, 2014	(691,752)		(691,752)
Common stock issued, Ending Balance (in shares) at Mar. 31, 2014	61,051,286	61,051,286