Loans, net and allowance for loan losses - Summarize Information in Concerning to Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	$ 9,896	$ 1,408	$ 1,489
Unpaid Principal Balance, With no related allowance, Total	17,681	1,408	1,489
Average Recorded Investment, With no related allowance, Total	9,956	1,573	1,578
Recorded Investment, With an allowance recorded, Total	4,378	3,863	2,045
Unpaid Principal Balance, With an allowance recorded, Total	4,378	3,863	2,045
Related Allowance, With an allowance recorded, Total	2,024	1,226	658
Average Recorded Investment, With an allowance recorded, Total	4,263	3,495	2,057
Interest Income Recognized, With an allowance recorded, Total	184	175	28
Recorded Investment, Total	14,274	5,271	3,534
Unpaid Principal Balance, Total	22,059	5,271	3,534
Average Recorded Investment, Total	14,219	5,068	3,635
Interest Income Recognized, Total	184	175	28
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	3,009	304
Unpaid Principal Balance, With no related allowance, Total	7,506	304
Average Recorded Investment, With no related allowance, Total	3,855	152
Recorded Investment, With an allowance recorded, Total	2,200	351	845
Unpaid Principal Balance, With an allowance recorded, Total	2,200	351	845
Related Allowance, With an allowance recorded, Total	1,500	351	443
Average Recorded Investment, With an allowance recorded, Total	2,182	351	1,000
Interest Income Recognized, With an allowance recorded, Total	95	17	28
Recorded Investment, Total	5,209	655	845
Unpaid Principal Balance, Total	9,706	655	845
Average Recorded Investment, Total	6,037	503	1,000
Interest Income Recognized, Total	95	17	28
Real Estate Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	3,923	145	591
Unpaid Principal Balance, With no related allowance, Total	6,777	145	591
Average Recorded Investment, With no related allowance, Total	3,522	201	390
Recorded Investment, With an allowance recorded, Total	1,394	2,015
Unpaid Principal Balance, With an allowance recorded, Total	1,394	2,015
Related Allowance, With an allowance recorded, Total	300	550
Average Recorded Investment, With an allowance recorded, Total	1,409	2,104
Interest Income Recognized, With an allowance recorded, Total	76	114
Recorded Investment, Total	5,317	2,160	591
Unpaid Principal Balance, Total	8,171	2,160	591
Average Recorded Investment, Total	4,931	2,305	390
Interest Income Recognized, Total	76	114
Real Estate Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	2,874	928	806
Unpaid Principal Balance, With no related allowance, Total	3,308	928	806
Average Recorded Investment, With no related allowance, Total	2,484	1,152	1,081
Recorded Investment, With an allowance recorded, Total	784	1,497	1,200
Unpaid Principal Balance, With an allowance recorded, Total	784	1,497	1,200
Related Allowance, With an allowance recorded, Total	224	325	215
Average Recorded Investment, With an allowance recorded, Total	672	1,040	1,057
Interest Income Recognized, With an allowance recorded, Total	13	44
Recorded Investment, Total	3,658	2,425	2,006
Unpaid Principal Balance, Total	4,092	2,425	2,006
Average Recorded Investment, Total	3,156	2,192	2,138
Interest Income Recognized, Total	13	44
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	90	31	92
Unpaid Principal Balance, With no related allowance, Total	90	31	92
Average Recorded Investment, With no related allowance, Total	95	68	107
Recorded Investment, With an allowance recorded, Total
Unpaid Principal Balance, With an allowance recorded, Total
Related Allowance, With an allowance recorded, Total
Average Recorded Investment, With an allowance recorded, Total
Interest Income Recognized, With an allowance recorded, Total
Recorded Investment, Total	90	31	92
Unpaid Principal Balance, Total	90	31	92
Average Recorded Investment, Total	95	68	107
Interest Income Recognized, Total

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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=28368275&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=28368275&loc=d3e5258-111524

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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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- 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=28368275&loc=SL6953550-111524

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Amount of allowance for credit losses related to recorded investment.

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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 a 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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