Allowance for Loan Losses - Investments in Loans Considered to be Impaired and Related Information on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	$ 47,619		$ 43,914
Without a related allowance, Unpaid Principal Balance	58,231		53,785
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	870		63
With a related allowance recorded, Unpaid Principal Balance	870		63
With a related allowance recorded, Related Allowance	88		54
Impaired Financing Receivable, Recorded Investment, Total	48,489		43,977
Impaired Financing Receivable, Unpaid Principal Balance, Total	59,101		53,848
Impaired Financing Receivable, Related Allowance	88		54
Without a related allowance recorded, Average Recorded Investment	48,285	50,068
Without a related allowance recorded, Interest Income Recognized	375	383
With a related allowance recorded, Average Recorded Investment	884	83
With a related allowance recorded, Interest Income Recognized	9	2
Impaired Financing Receivable, Average Recorded Investment, Total	49,169	50,151
Impaired Financing Receivable, Interest Income Recognized, Total	384	385
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	22,515		19,890
Without a related allowance, Unpaid Principal Balance	27,937		25,262
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	811		0
With a related allowance recorded, Unpaid Principal Balance	811		0
With a related allowance recorded, Related Allowance	39		0
Impaired Financing Receivable, Recorded Investment, Total	23,326		19,890
Impaired Financing Receivable, Unpaid Principal Balance, Total	28,748		25,262
Impaired Financing Receivable, Related Allowance	39		0
Without a related allowance recorded, Average Recorded Investment	22,627	23,539
Without a related allowance recorded, Interest Income Recognized	164	167
With a related allowance recorded, Average Recorded Investment	823	0
With a related allowance recorded, Interest Income Recognized	8	0
Impaired Financing Receivable, Average Recorded Investment, Total	23,450	23,539
Impaired Financing Receivable, Interest Income Recognized, Total	172	167
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	10,338		9,218
Without a related allowance, Unpaid Principal Balance	11,238		9,449
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	0		0
With a related allowance recorded, Unpaid Principal Balance	0		0
With a related allowance recorded, Related Allowance	0		0
Impaired Financing Receivable, Recorded Investment, Total	10,338		9,218
Impaired Financing Receivable, Unpaid Principal Balance, Total	11,238		9,449
Impaired Financing Receivable, Related Allowance	0		0
Without a related allowance recorded, Average Recorded Investment	10,847	9,826
Without a related allowance recorded, Interest Income Recognized	62	55
With a related allowance recorded, Average Recorded Investment	0	0
With a related allowance recorded, Interest Income Recognized	0	0
Impaired Financing Receivable, Average Recorded Investment, Total	10,847	9,826
Impaired Financing Receivable, Interest Income Recognized, Total	62	55
Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	7,696		7,605
Without a related allowance, Unpaid Principal Balance	11,385		11,293
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	0		0
With a related allowance recorded, Unpaid Principal Balance	0		0
With a related allowance recorded, Related Allowance	0		0
Impaired Financing Receivable, Recorded Investment, Total	7,696		7,605
Impaired Financing Receivable, Unpaid Principal Balance, Total	11,385		11,293
Impaired Financing Receivable, Related Allowance	0		0
Without a related allowance recorded, Average Recorded Investment	7,704	8,324
Without a related allowance recorded, Interest Income Recognized	53	57
With a related allowance recorded, Average Recorded Investment	0	0
With a related allowance recorded, Interest Income Recognized	0	0
Impaired Financing Receivable, Average Recorded Investment, Total	7,704	8,324
Impaired Financing Receivable, Interest Income Recognized, Total	53	57
Consumer Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	7,039		7,159
Without a related allowance, Unpaid Principal Balance	7,637		7,733
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	41		43
With a related allowance recorded, Unpaid Principal Balance	41		43
With a related allowance recorded, Related Allowance	41		43
Impaired Financing Receivable, Recorded Investment, Total	7,080		7,202
Impaired Financing Receivable, Unpaid Principal Balance, Total	7,678		7,776
Impaired Financing Receivable, Related Allowance	41		43
Without a related allowance recorded, Average Recorded Investment	7,073	8,258
Without a related allowance recorded, Interest Income Recognized	96	103
With a related allowance recorded, Average Recorded Investment	42	51
With a related allowance recorded, Interest Income Recognized	1	1
Impaired Financing Receivable, Average Recorded Investment, Total	7,115	8,309
Impaired Financing Receivable, Interest Income Recognized, Total	97	104
Other Consumer [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	31		42
Without a related allowance, Unpaid Principal Balance	34		48
Without a related allowance recorded, Related Allowance	0		0
With a related allowance recorded, Recorded Investment	18		20
With a related allowance recorded, Unpaid Principal Balance	18		20
With a related allowance recorded, Related Allowance	8		11
Impaired Financing Receivable, Recorded Investment, Total	49		62
Impaired Financing Receivable, Unpaid Principal Balance, Total	52		68
Impaired Financing Receivable, Related Allowance	8		11
Without a related allowance recorded, Average Recorded Investment	34	121
Without a related allowance recorded, Interest Income Recognized	0	1
With a related allowance recorded, Average Recorded Investment	19	32
With a related allowance recorded, Interest Income Recognized	0	1
Impaired Financing Receivable, Average Recorded Investment, Total	53	153
Impaired Financing Receivable, Interest Income Recognized, Total	$ 0	$ 2

Impaired financing receivable with no related allowance.

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+ References

No definition available.

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- Definition

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 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=35738203&loc=SL6953550-111524

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

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- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

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- Definition

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

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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.

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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.

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Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

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