Consolidated Statements of Shareholders' Equity (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, 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
Net income	0	0	0	84,295	84,295
Change in fair value of available-for-sale securities, net of tax effect	0	0	1,599	0	1,599
Change in pension funding status, net of tax effect	0	0	(7,984)	0	(7,984)
Comprehensive income					77,910
Issuance of stock	27,381	81,296			108,677
Issuance of stock (in shares)	10,952,381
Exercise of stock options	17	67	0	0	84
Exercise of stock options (in shares)	6,533
Income tax benefit (expense) from exercise of stock options	0	(32)	0	0	(32)
Recognition of stock compensation	281	3,073	0	0	3,354
Repurchase of stock	(13)	(62)			(75)
Repurchase of stock (in shares)	(5,158)
Cash dividends declared	0	0	0	(3,778)	(3,778)
Balance at Dec. 31, 2012	$ 236,375	$ 311,909	$ (8,646)	$ 909,414	$ 1,449,052
Balance (in shares) at Dec. 31, 2012	94,437,552