Organization and significant accounting policies (Details) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Organization and significant accounting policies [Abstract]
Stock Conversion Ratio	0.87423
Loans receivable [Abstract]
Accrual of interest discontinuation, Minimum	3 months
Loans charge off period, Maximum	120 days
Loan return to accrual status	12 months
Federal Home Loan Bank Stock [Abstract]
Minimum Required Investment in Federal Home Loan Bank Stock	$ 984,000	$ 383,000
Segment Reporting [Abstract]
Number of operating segments	1
Advertising Cost [Abstract]
Advertising costs	263,000	98,000
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful lives	9 years 6 months
Acquired finite lived intangible assets remaining life	6 years 2 months 12 days
Employee Stock Ownership Plan [Abstract]
Unallocated shares (in shares)	152,572
Committed to release (in shares)	21,443
Earnings Per Common Share [Abstract]
Weighted average number of common shares outstanding (in shares)	2,586,159	2,581,966
Share-based compensation arrangement, fair value assumptions and methodology [Abstract]
Annual dividend yield (in hundredths)	0.00%
Expected volatility (in hundredths)	28.97%
Risk-free interest rate (in hundredths)	1.46%
Expected term	7 years 6 months
Core Deposits [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible asset	$ 753,000	$ 875,000
Furniture and equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life	1 year
Furniture and equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life	10 years

The minimum period for the discontinuation of accrual of interest on past due loans.

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Remaining life of finite-lived intangible assets acquired either individually or as part of a group of assets.

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The number of months consecutive timely payments for loans to return to accrual status.

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The maximum past due period for charge off of loans unless secured by collateral.

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- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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Ratio of stock to be issued in stock exchange.

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The aggregate amount assigned to a major class of finite-lived intangible assets acquired either individually or as part of a group of assets (in either an asset acquisition or business combination). A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(1)

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 44

-Subparagraph a(1)

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Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 720

-SubTopic 35

-Section 50

-Paragraph 1

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-Publisher AICPA

-Name Statement of Position (SOP)

-Number 93-7

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The shares that, although not legally released, will be released by a future scheduled and committed debt service payment and will be allocated to employees for service rendered in the current accounting period. The ESOP documents typically define the period of service to which the shares relate. ESOP shares are released to compensate employees directly, to settle employer liabilities for other employee benefits, and to replace dividends on allocated shares that are used for debt service.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 40

-Section 50

-Paragraph 1

-Subparagraph (d)

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-Name Statement of Position (SOP)

-Number 93-6

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Shares contributed to the ESOP that have not yet been released, committed to be released, or allocated to participant accounts. Suspense shares generally collateralize ESOP debt.

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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (f)(2)(iii)

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-Number 123R

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section D

-Subsection 2

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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-Paragraph 40

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-Name Emerging Issues Task Force (EITF)

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