Loans - Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 67,017	$ 69,656
Recorded Investment With No Allowance	46,942	50,473
Recorded Investment With Allowance	2,917	3,118
Total Recorded Investment	49,859	53,591
Related Allowance	1,475	1,680
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	705	706
Recorded Investment With No Allowance	636	636
Recorded Investment With Allowance	0	0
Total Recorded Investment	636	636
Related Allowance	0	0
Commercial and industrial, Other commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	42,262	42,212
Recorded Investment With No Allowance	28,275	29,007
Recorded Investment With Allowance	2,720	2,853
Total Recorded Investment	30,995	31,860
Related Allowance	1,404	1,613
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	20,257	22,919
Recorded Investment With No Allowance	14,723	17,441
Recorded Investment With Allowance	197	265
Total Recorded Investment	14,920	17,706
Related Allowance	71	67
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	3,004	3,007
Recorded Investment With No Allowance	2,740	2,793
Recorded Investment With Allowance	0	0
Total Recorded Investment	2,740	2,793
Related Allowance	0	0
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	789	812
Recorded Investment With No Allowance	568	596
Recorded Investment With Allowance	0	0
Total Recorded Investment	568	596
Related Allowance	0	0
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	0	0
Recorded Investment With No Allowance	0	0
Recorded Investment With Allowance	0	0
Total Recorded Investment	0	0
Related Allowance	$ 0	$ 0

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953550-111524

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

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- Definition

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(4)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

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