Loans and Allowance - Allowance for Credit Losses and Loan Portfolio by Loan Segment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 4,243	$ 7,938
Collectively evaluated for impairment	65,123	62,960
Total Allowance for Loan Losses	69,366	70,898	82,977	92,131
Individually evaluated for impairment	68,099	83,319
Collectively evaluated for impairment	2,821,358	2,630,096
Financing Receivable, Acquired with Deteriorated Credit Quality	12,752
Loans	2,902,209	2,713,415
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,628	4,701
Collectively evaluated for impairment	24,285	13,030
Total Allowance for Loan Losses	25,913	17,731	32,508	48,770
Individually evaluated for impairment	14,190	18,793
Collectively evaluated for impairment	765,707	657,761
Financing Receivable, Acquired with Deteriorated Credit Quality	1,710
Loans	781,607	676,554
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	2,565	2,504
Collectively evaluated for impairment	24,138	35,415
Total Allowance for Loan Losses	26,703	37,919	36,341	30,189
Individually evaluated for impairment	45,394	51,980
Collectively evaluated for impairment	1,309,912	1,224,030
Financing Receivable, Acquired with Deteriorated Credit Quality	10,015
Loans	1,365,321	1,276,010
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment	2,593	2,902
Total Allowance for Loan Losses	2,593	2,902	3,622	2,242
Collectively evaluated for impairment	75,748	84,172
Loans	75,748	84,172
Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	50	733
Collectively evaluated for impairment	14,107	11,610
Total Allowance for Loan Losses	14,157	12,343	10,408	10,751
Individually evaluated for impairment	8,515	12,546
Collectively evaluated for impairment	667,401	660,578
Financing Receivable, Acquired with Deteriorated Credit Quality	1,027
Loans	676,943	673,124
Finance Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment		3
Total Allowance for Loan Losses		3	98	179
Collectively evaluated for impairment	2,590	3,555
Loans	$ 2,590	$ 3,555