Allowance for Loan Losses - Investments in Loans Considered to be Impaired and Related Information on Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
With a related allowance recorded, Recorded Investment	$ 618	$ 63
With a related allowance recorded, Unpaid Principal Balance	1,468	63
With a related allowance recorded, Related Allowance	37	54
Without a related allowance recorded, Recorded Investment	45,032	43,914
Without a related allowance, Unpaid Principal Balance	50,286	53,785
Without a related allowance recorded, Related Allowance	0	0
Impaired financing receivables	45,650	43,977
Impaired Financing Receivable, Unpaid Principal Balance, Total	51,754	53,848
Impaired Financing Receivable, Related Allowance, Total	37	54
With a related allowance recorded, Average Recorded Investment	956	72
With a related allowance recorded, Interest Income Recognized	7	6
Without a related allowance recorded, Average Recorded Investment	46,638	44,978
Without a related allowance recorded, Interest Income Recognized	1,741	1,550
Impaired Financing Receivable, Average Recorded Investment, Total	47,594	45,050
Impaired Financing Receivable, Interest Income Recognized, Total	1,748	1,556
Commercial Real Estate
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	12,661	19,890
Without a related allowance, Unpaid Principal Balance	13,157	25,262
Without a related allowance recorded, Related Allowance	0	0
Impaired financing receivables	12,661	19,890
Impaired Financing Receivable, Unpaid Principal Balance, Total	13,157	25,262
Impaired Financing Receivable, Related Allowance, Total	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	14,622	20,504
Without a related allowance recorded, Interest Income Recognized	597	684
Impaired Financing Receivable, Average Recorded Investment, Total	14,622	20,504
Impaired Financing Receivable, Interest Income Recognized, Total	597	684
Commercial and Industrial
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	14,417	9,218
Without a related allowance, Unpaid Principal Balance	15,220	9,449
Without a related allowance recorded, Related Allowance	0	0
Impaired financing receivables	14,417	9,218
Impaired Financing Receivable, Unpaid Principal Balance, Total	15,220	9,449
Impaired Financing Receivable, Related Allowance, Total	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	14,416	9,246
Without a related allowance recorded, Interest Income Recognized	450	241
Impaired Financing Receivable, Average Recorded Investment, Total	14,416	9,246
Impaired Financing Receivable, Interest Income Recognized, Total	450	241
Commercial Construction
Financing Receivable, Impaired [Line Items]
With a related allowance recorded, Recorded Investment	500	0
With a related allowance recorded, Unpaid Principal Balance	1,350	0
With a related allowance recorded, Related Allowance	3	0
Without a related allowance recorded, Recorded Investment	10,998	7,605
Without a related allowance, Unpaid Principal Balance	14,200	11,293
Without a related allowance recorded, Related Allowance	0	0
Impaired financing receivables	11,498	7,605
Impaired Financing Receivable, Unpaid Principal Balance, Total	15,550	11,293
Impaired Financing Receivable, Related Allowance, Total	3	0
With a related allowance recorded, Average Recorded Investment	834	0
With a related allowance recorded, Interest Income Recognized	0	0
Without a related allowance recorded, Average Recorded Investment	10,581	8,145
Without a related allowance recorded, Interest Income Recognized	329	227
Impaired Financing Receivable, Average Recorded Investment, Total	11,415	8,145
Impaired Financing Receivable, Interest Income Recognized, Total	329	227
Consumer Real Estate
Financing Receivable, Impaired [Line Items]
With a related allowance recorded, Recorded Investment	116	43
With a related allowance recorded, Unpaid Principal Balance	116	43
With a related allowance recorded, Related Allowance	32	43
Without a related allowance recorded, Recorded Investment	6,845	7,159
Without a related allowance, Unpaid Principal Balance	7,521	7,733
Without a related allowance recorded, Related Allowance	0	0
Impaired financing receivables	6,961	7,202
Impaired Financing Receivable, Unpaid Principal Balance, Total	7,637	7,776
Impaired Financing Receivable, Related Allowance, Total	32	43
With a related allowance recorded, Average Recorded Investment	120	48
With a related allowance recorded, Interest Income Recognized	7	4
Without a related allowance recorded, Average Recorded Investment	6,902	7,027
Without a related allowance recorded, Interest Income Recognized	364	396
Impaired Financing Receivable, Average Recorded Investment, Total	7,022	7,075
Impaired Financing Receivable, Interest Income Recognized, Total	371	400
Other Consumer
Financing Receivable, Impaired [Line Items]
With a related allowance recorded, Recorded Investment	2	20
With a related allowance recorded, Unpaid Principal Balance	2	20
With a related allowance recorded, Related Allowance	2	11
Without a related allowance recorded, Recorded Investment	111	42
Without a related allowance, Unpaid Principal Balance	188	48
Without a related allowance recorded, Related Allowance	0	0
Impaired financing receivables	113	62
Impaired Financing Receivable, Unpaid Principal Balance, Total	190	68
Impaired Financing Receivable, Related Allowance, Total	2	11
With a related allowance recorded, Average Recorded Investment	2	24
With a related allowance recorded, Interest Income Recognized	0	2
Without a related allowance recorded, Average Recorded Investment	117	56
Without a related allowance recorded, Interest Income Recognized	1	2
Impaired Financing Receivable, Average Recorded Investment, Total	119	80
Impaired Financing Receivable, Interest Income Recognized, Total	$ 1	$ 4

Impaired financing receivable with no related allowance.

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No definition available.

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No definition available.

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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=49124121&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=49124121&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.

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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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Amount of allowance for credit losses related to recorded investment.

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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.

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Amount of average investment of impaired financing receivables for which there is no 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 17
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5258-111524

Reference 2: 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=49124121&loc=d3e5212-111524

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

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