Allowance for Loan Losses - Investments in Loans Considered to be Impaired and Related Information on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
With a related allowance recorded, Recorded Investment	$ 63	$ 767
With a related allowance recorded, Unpaid Principal Balance	63	1,469
With a related allowance recorded, Related Allowance	54	97
Without a related allowance recorded, Recorded Investment	43,914	52,089
Without a related allowance, Unpaid Principal Balance	53,785	67,122
Without a related allowance recorded, Related Allowance	0	0
Impaired Financing Receivable, Recorded Investment, Total	43,977	52,856
Impaired Financing Receivable, Unpaid Principal Balance, Total	53,848	68,591
Impaired Financing Receivable, Related Allowance	54	97
With a related allowance recorded, Average Recorded Investment	72	3,631
With a related allowance recorded, Interest Income Recognized	6	59
Without a related allowance recorded, Average Recorded Investment	44,978	63,693
Without a related allowance recorded, Interest Income Recognized	1,550	1,951
Impaired Financing Receivable, Average Recorded Investment, Total	45,050	67,324
Impaired Financing Receivable, Interest Income Recognized, Total	1,556	2,010
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
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
Without a related allowance recorded, Recorded Investment	19,890	26,968
Without a related allowance, Unpaid Principal Balance	25,262	35,474
Without a related allowance recorded, Related Allowance	0	0
Impaired Financing Receivable, Recorded Investment, Total	19,890	26,968
Impaired Financing Receivable, Unpaid Principal Balance, Total	25,262	35,474
Impaired Financing Receivable, Related Allowance	0	0
With a related allowance recorded, Average Recorded Investment	0	1,895
With a related allowance recorded, Interest Income Recognized	0	0
Without a related allowance recorded, Average Recorded Investment	20,504	29,314
Without a related allowance recorded, Interest Income Recognized	684	929
Impaired Financing Receivable, Average Recorded Investment, Total	20,504	31,209
Impaired Financing Receivable, Interest Income Recognized, Total	684	929
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
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
Without a related allowance recorded, Recorded Investment	9,218	9,580
Without a related allowance, Unpaid Principal Balance	9,449	9,703
Without a related allowance recorded, Related Allowance	0	0
Impaired Financing Receivable, Recorded Investment, Total	9,218	9,580
Impaired Financing Receivable, Unpaid Principal Balance, Total	9,449	9,703
Impaired Financing Receivable, Related Allowance	0	0
With a related allowance recorded, Average Recorded Investment	0	0
With a related allowance recorded, Interest Income Recognized	0	0
Without a related allowance recorded, Average Recorded Investment	9,246	11,439
Without a related allowance recorded, Interest Income Recognized	241	254
Impaired Financing Receivable, Average Recorded Investment, Total	9,246	11,439
Impaired Financing Receivable, Interest Income Recognized, Total	241	254
Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
With a related allowance recorded, Recorded Investment	0	681
With a related allowance recorded, Unpaid Principal Balance	0	1,383
With a related allowance recorded, Related Allowance	0	25
Without a related allowance recorded, Recorded Investment	7,605	7,391
Without a related allowance, Unpaid Principal Balance	11,293	12,353
Without a related allowance recorded, Related Allowance	0	0
Impaired Financing Receivable, Recorded Investment, Total	7,605	8,072
Impaired Financing Receivable, Unpaid Principal Balance, Total	11,293	13,736
Impaired Financing Receivable, Related Allowance	0	25
With a related allowance recorded, Average Recorded Investment	0	1,652
With a related allowance recorded, Interest Income Recognized	0	49
Without a related allowance recorded, Average Recorded Investment	8,145	14,112
Without a related allowance recorded, Interest Income Recognized	227	326
Impaired Financing Receivable, Average Recorded Investment, Total	8,145	15,764
Impaired Financing Receivable, Interest Income Recognized, Total	227	375
Consumer Real Estate [Member]
Financing Receivable, Impaired [Line Items]
With a related allowance recorded, Recorded Investment	43	53
With a related allowance recorded, Unpaid Principal Balance	43	53
With a related allowance recorded, Related Allowance	43	53
Without a related allowance recorded, Recorded Investment	7,159	8,026
Without a related allowance, Unpaid Principal Balance	7,733	9,464
Without a related allowance recorded, Related Allowance	0	0
Impaired Financing Receivable, Recorded Investment, Total	7,202	8,079
Impaired Financing Receivable, Unpaid Principal Balance, Total	7,776	9,517
Impaired Financing Receivable, Related Allowance	43	53
With a related allowance recorded, Average Recorded Investment	48	60
With a related allowance recorded, Interest Income Recognized	4	6
Without a related allowance recorded, Average Recorded Investment	7,027	8,714
Without a related allowance recorded, Interest Income Recognized	396	436
Impaired Financing Receivable, Average Recorded Investment, Total	7,074	8,774
Impaired Financing Receivable, Interest Income Recognized, Total	400	442
Other Consumer [Member]
Financing Receivable, Impaired [Line Items]
With a related allowance recorded, Recorded Investment	20	33
With a related allowance recorded, Unpaid Principal Balance	20	33
With a related allowance recorded, Related Allowance	11	19
Without a related allowance recorded, Recorded Investment	42	124
Without a related allowance, Unpaid Principal Balance	48	128
Without a related allowance recorded, Related Allowance	0	0
Impaired Financing Receivable, Recorded Investment, Total	62	157
Impaired Financing Receivable, Unpaid Principal Balance, Total	68	161
Impaired Financing Receivable, Related Allowance	11	19
With a related allowance recorded, Average Recorded Investment	24	24
With a related allowance recorded, Interest Income Recognized	2	4
Without a related allowance recorded, Average Recorded Investment	56	114
Without a related allowance recorded, Interest Income Recognized	2	6
Impaired Financing Receivable, Average Recorded Investment, Total	81	138
Impaired Financing Receivable, Interest Income Recognized, Total	$ 4	$ 10

Impaired financing receivable with no related allowance.

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- Definition

Impaired financing receivable with related allowance related allowance.

+ 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

+ Details

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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.

+ 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

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- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

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- Definition

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

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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.

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

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- Definition

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

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