Allowance for Credit Losses and Loan Portfolio by Loan Segment (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 3,508	$ 4,243
Collectively evaluated for impairment	64,915	65,123
Loans acquired with deteriorated credit quality	114
Total Allowance for Loan Losses	68,537	69,366	70,369	70,898
Individually evaluated for impairment	57,987	68,099
Collectively evaluated for impairment	2,810,125	2,821,358
Loans acquired with deteriorated credit quality	11,430	12,752
Loans	2,879,542	2,902,209
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	838	1,628
Collectively evaluated for impairment	24,533	24,285
Total Allowance for Loan Losses	25,371	25,913	15,574	17,731
Individually evaluated for impairment	11,057	14,190
Collectively evaluated for impairment	766,238	765,707
Loans acquired with deteriorated credit quality	1,037	1,710
Loans	778,332	781,607
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	2,373	2,565
Collectively evaluated for impairment	22,508	24,138
Loans acquired with deteriorated credit quality	97
Total Allowance for Loan Losses	24,978	26,703	37,907	37,919
Individually evaluated for impairment	39,154	45,394
Collectively evaluated for impairment	1,307,663	1,309,912
Loans acquired with deteriorated credit quality	9,669	10,015
Loans	1,356,486	1,365,321
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment	2,689	2,593
Total Allowance for Loan Losses	2,689	2,593	2,805	2,902
Collectively evaluated for impairment	73,314	75,748
Loans acquired with deteriorated credit quality
Loans	73,314	75,748
Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	297	50
Collectively evaluated for impairment	15,165	14,107
Loans acquired with deteriorated credit quality	17
Total Allowance for Loan Losses	15,479	14,157	14,083	12,343
Individually evaluated for impairment	7,776	8,515
Collectively evaluated for impairment	660,897	667,401
Loans acquired with deteriorated credit quality	724	1,027
Loans	669,397	676,943
Finance Lease
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment	20
Total Allowance for Loan Losses	20		0	3
Collectively evaluated for impairment	2,013	2,590
Loans acquired with deteriorated credit quality
Loans	$ 2,013	$ 2,590