Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current [Abstract]
Federal	$ 29,274,000	$ 34,124,000	$ 21,046,000
State	1,477,000	1,743,000	1,086,000
Current tax expense (benefit)	30,751,000	35,867,000	22,132,000
Deferred [Abstract]
Federal	(8,129,000)	(12,121,000)	(1,669,000)
State	(1,349,000)	(2,834,000)	168,000
Deferred tax expense (benefit)	(9,478,000)	(14,955,000)	(1,501,000)
Income tax expense	21,273,000	20,912,000	20,631,000
Income tax recorded to stockholders' equity	(500,000)	(4,300,000)	6,100,000
Deferred tax assets [Abstract]
Allowance for loan and lease losses	27,487,000	27,463,000
Deferred compensation	4,911,000	4,653,000
Postretirement benefit obligation	1,036,000	1,024,000
Purchase accounting fair value adjustments	2,227,000	0
Accrued liabilities	1,482,000	1,649,000
Stock-based compensation expense	4,440,000	3,943,000
Other	1,214,000	1,012,000
Total deferred tax assets	42,797,000	39,744,000
Deferred tax liabilities [Abstract]
Pension and executive retirement	6,916,000	11,922,000
Unrealized gains on securities available for sale	12,156,000	7,162,000
Premises and equipment, primarily due to accelerated depreciation	2,340,000	1,384,000
Equipment leasing	3,090,000	11,456,000
Deferred loan costs	767,000	1,395,000
Intangible amortization	11,081,000	10,270,000
Other	494,000	178,000
Total deferred tax liabilities	36,844,000	43,767,000
Net deferred tax liability at period-end	5,953,000	(4,023,000)	(23,245,000)
Net deferred tax liability at beginning of period	(4,023,000)	(23,245,000)
(Decrease) increase in net deferred tax liability	(9,976,000)	(19,222,000)
Reconciliation of gross unrecognized tax benefits [Roll Forward]
Balance, beginning of period	3,081,000	2,287,000	2,212,000
Additions for tax positions of prior years	0	1,714,000	132,000
Reduction for tax positions of prior years	(2,193,000)	(920,000)	(57,000)
Balance, end of period	888,000	3,081,000	2,287,000
Unrecognized tax benefits that would impact effective tax rate, if recognized	900,000	3,100,000	2,300,000
Decreases in unrecognized tax benefits resulting from settlements with taxing authorities	1,400,000	800,000
Decrease in tax expense resulting from lapse of statute of limitations	1,500,000
Accrued interest	100,000	700,000
Net interest	300,000	100,000	200,000
Federal statutory income tax rate (in hundredths)	35.00%
Income tax reconciliation [Abstract]
Federal income tax at statutory rate	27,711,000	27,410,000	25,424,000
Tax exempt income	(2,925,000)	(3,448,000)	(3,811,000)
Net increase in CSV of life insurance	(919,000)	(939,000)	(871,000)
Low income housing tax credits	(782,000)	(296,000)	(132,000)
State taxes, net of federal tax benefit	764,000	756,000	816,000
State audit settlements and law change	(681,000)	(1,465,000)	0
Other, net	(1,895,000)	(1,106,000)	(795,000)
Income tax expense	$ 21,273,000	$ 20,912,000	$ 20,631,000