Consolidated Statements Of Changes In Equity (USD $) In Thousands	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non-Controlling Interest [Member]	Total
Balance at Dec. 31, 2008	$ 379,505	$ 621,458	$ 633,159	$ (761)	$ (56,729)	$ 2,835	$ 1,579,467
Net income			169,075			(700)	168,375
Change in unrealized gain (loss) related to available for sale securities for which a portion of an other-than-temporary impairment has been recorded in earnings, net of tax					7,596		7,596
Change in unrealized gain (loss) on all other available for sale securities, net of tax					93,075		93,075
Change related to pension plan, net of tax					2,465		2,465
Total comprehensive income							271,511
Distributions to non-controlling interest						(458)	(458)
Purchase of treasury stock				(528)			(528)
Cash dividends paid			(74,720)				(74,720)
Net tax benefit related to equity compensation plans		557					557
Stock-based compensation		6,642					6,642
Issuance under stock purchase and equity compensation plans, net	1,910	3,127		451			5,488
Issuance of stock under open market sale program	14,474	83,679					98,153
5% stock dividend, net	19,748	139,027	(158,982)				(207)
Balance at Dec. 31, 2009	415,637	854,490	568,532	(838)	46,407	1,677	1,885,905
Net income			221,710			165	221,875
Change in unrealized gain (loss) related to available for sale securities for which a portion of an other-than-temporary impairment has been recorded in earnings, net of tax					14,243		14,243
Change in unrealized gain (loss) on all other available for sale securities, net of tax					1,813		1,813
Change related to pension plan, net of tax					882		882
Total comprehensive income							238,813
Distributions to non-controlling interest						(365)	(365)
Purchase of treasury stock				(40,984)			(40,984)
Cash dividends paid			(78,231)				(78,231)
Net tax benefit related to equity compensation plans		1,178					1,178
Stock-based compensation		6,021					6,021
Issuance under stock purchase and equity compensation plans, net	2,196	3,102		6,012			11,310
5% stock dividend, net	16,109	106,502	(156,233)	33,439			(183)
Balance at Dec. 31, 2010	433,942	971,293	555,778	(2,371)	63,345	1,477	2,023,464
Net income			256,343			3,280	259,623
Change in unrealized gain (loss) related to available for sale securities for which a portion of an other-than-temporary impairment has been recorded in earnings, net of tax					3,214		3,214
Change in unrealized gain (loss) on all other available for sale securities, net of tax					48,287		48,287
Change related to pension plan, net of tax					(4,308)		(4,308)
Total comprehensive income							306,816
Distributions to non-controlling interest						(443)	(443)
Purchase of treasury stock				(101,154)			(101,154)
Cash dividends paid			(79,140)				(79,140)
Net tax benefit related to equity compensation plans		1,065					1,065
Stock-based compensation		4,731					4,731
Issuance under stock purchase and equity compensation plans, net	2,539	4,061		8,749			15,349
5% stock dividend, net	9,906	60,915	(157,562)	86,414			(327)
Balance at Dec. 31, 2011	$ 446,387	$ 1,042,065	$ 575,419	$ (8,362)	$ 110,538	$ 4,314	$ 2,170,361