Consolidated Statements of Shareholders' Equity and Comprehensive Income (USD $) In Thousands, except Share data	Common Stock [Member]	Capital Surplus [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2008	$ 207,763	$ 215,255	$ (26,896)	$ 844,138	$ 1,240,260
Balance (in shares) at Dec. 31, 2008	83,105,100
Net income	0	0	0	82,729	82,729
Change in fair value of available-for-sale securities, net of tax effect	0	0	7,057	0	7,057
Change in pension funding status, net of tax effect	0	0	11,430	0	11,430
Comprehensive income					101,216
Exercise of stock options	853	5,467	0	0	6,320
Exercise of stock options (in shares)	341,089
Income tax benefit (expense) from exercise of stock options	0	500	0	0	500
Recognition of stock compensation	10	1,325	0	0	1,335
Recognition of stock compensation (in shares)	4,107
Cash dividends declared	0	0	0	(73,335)	(73,335)
Balance at Dec. 31, 2009	208,626	222,547	(8,409)	853,532	1,276,296
Balance (in shares) at Dec. 31, 2009	83,450,296
Net income	0	0	0	22,942	22,942
Change in fair value of available-for-sale securities, net of tax effect	0	0	(5,165)	0	(5,165)
Change in pension funding status, net of tax effect	0	0	(879)	0	(879)
Comprehensive income					16,898
Exercise of stock options	65	355	0	0	420
Exercise of stock options (in shares)	26,441
Income tax benefit (expense) from exercise of stock options	0	44	0	0	44
Recognition of stock compensation	13	2,030	0	0	2,043
Recognition of stock compensation (in shares)	5,000
Cash dividends declared	0	0	0	(73,457)	(73,457)
Balance at Dec. 31, 2010	208,704	224,976	(14,453)	803,017	1,222,244
Balance (in shares) at Dec. 31, 2010	83,481,737
Net income	0	0	0	37,569	37,569
Change in fair value of available-for-sale securities, net of tax effect	0	0	26,989	0	26,989
Change in pension funding status, net of tax effect	0	0	(14,797)	0	(14,797)
Comprehensive income					49,761
Exercise of stock options	5	15	0	0	20
Exercise of stock options (in shares)	2,217
Income tax benefit (expense) from exercise of stock options	0	(50)	0	0	(50)
Recognition of stock compensation	13	2,670	0	0	2,683
Recognition of stock compensation (in shares)	5,000
Repurchase of stock	(13)	(44)			(57)
Repurchase of stock (in shares)	(5,158)
Cash dividends declared	0	0	0	(11,689)	(11,689)
Balance at Dec. 31, 2011	$ 208,709	$ 227,567	$ (2,261)	$ 828,897	$ 1,262,912
Balance (in shares) at Dec. 31, 2011	83,483,796