Loans, net and allowance for loan losses - Allocation of Allowance for Loan Losses and Related Loans by Major Classification of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Allowance for loan losses:
Ending balance: individually evaluated for impairment	$ 3,480	$ 2,682
Ending balance: collectively evaluated for impairment	7,841	7,379
Loans receivable:
Ending balance	1,231,541	1,209,894
Ending balance: individually evaluated for impairment	12,550	11,807
Ending balance: collectively evaluated for impairment	1,216,538	1,195,303
Loans Acquired with Deteriorated Credit Quality [Member]
Loans receivable:
Ending balance	2,453	2,784
Commercial [Member]
Allowance for loan losses:
Ending balance: individually evaluated for impairment	1,209	1,072
Ending balance: collectively evaluated for impairment	1,226	1,081
Loans receivable:
Ending balance	322,418	319,590
Ending balance: individually evaluated for impairment	1,948	2,595
Ending balance: collectively evaluated for impairment	319,448	315,642
Commercial [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Loans receivable:
Ending balance	1,022	1,353
Real Estate Commercial [Member]
Allowance for loan losses:
Ending balance: individually evaluated for impairment	1,338	805
Ending balance: collectively evaluated for impairment	1,745	2,125
Loans receivable:
Ending balance	511,835	493,481
Ending balance: individually evaluated for impairment	6,080	5,084
Ending balance: collectively evaluated for impairment	504,379	487,024
Real Estate Commercial [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Loans receivable:
Ending balance	1,376	1,373
Real Estate Residential [Member]
Allowance for loan losses:
Ending balance: individually evaluated for impairment	796	767
Ending balance: collectively evaluated for impairment	3,231	2,921
Loans receivable:
Ending balance	312,567	310,667
Ending balance: individually evaluated for impairment	4,385	4,001
Ending balance: collectively evaluated for impairment	308,127	306,608
Real Estate Residential [Member] \| Loans Acquired with Deteriorated Credit Quality [Member]
Loans receivable:
Ending balance	55	58
Consumer [Member]
Allowance for loan losses:
Ending balance: individually evaluated for impairment	137	38
Ending balance: collectively evaluated for impairment	1,639	1,252
Loans receivable:
Ending balance	84,721	86,156
Ending balance: individually evaluated for impairment	137	127
Ending balance: collectively evaluated for impairment	$ 84,584	$ 86,029

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

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- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (h)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

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The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (h)

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

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Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3)

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