Loans and Allowance for Credit Losses - Schedule of Average Balance and Interest Income Recognized on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Average Recorded Investment, Total	$ 94,755	$ 70,266
Interest Income Recognized	261	284
Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	26,849	17,151
Interest Income Recognized with no related allowance	42	33
Average Recorded Investment with an allowance recorded	11,516	11,045
Interest Income Recognized with an allowance recorded	48	54
Commercial Real Estate - Construction [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	2,250	1,007
Interest Income Recognized with no related allowance	3
Average Recorded Investment with an allowance recorded	166
Commercial Real Estate - Other [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	38,801	17,542
Interest Income Recognized with no related allowance	85	54
Average Recorded Investment with an allowance recorded	10,728	19,851
Interest Income Recognized with an allowance recorded	1	112
Consumer Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	731	394
Interest Income Recognized with no related allowance	1	2
Average Recorded Investment with an allowance recorded	1,492	975
Interest Income Recognized with an allowance recorded	20	12
Residential [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment with no related allowance	747	116
Average Recorded Investment with an allowance recorded	1,475	2,185
Interest Income Recognized with an allowance recorded	$ 61	$ 17

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Average 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 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5258-111524

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- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

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- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

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- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

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- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

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- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

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