Fair value measurement of assets and liabilities - Fair Value Measurements at Reported Date (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Recurring fair value measurements \| Investments
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	$ 100,550	$ 95,058
Recurring fair value measurements \| U.S. government agency securities
Assets and Liabilities Measured at Fair Value
Investment securities available for sale
Recurring fair value measurements \| US Government-sponsored Enterprises Debt Securities [Member]
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	9,964	9,151
Recurring fair value measurements \| Obligations of state and political subdivisions
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	24,694	13,027
Recurring fair value measurements \| Mortgage-backed securities
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	3,575	3,500
Recurring fair value measurements \| Corporate Securities
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	54,201	60,432
Recurring fair value measurements \| Equity Securities [Member]
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	5,488	6,207
Recurring fair value measurements \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	9,964	9,151
Recurring fair value measurements \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| US Government-sponsored Enterprises Debt Securities [Member]
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	9,964	9,151
Recurring fair value measurements \| Significant Other Observable Inputs (Level 2)
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	90,202	85,495
Recurring fair value measurements \| Significant Other Observable Inputs (Level 2) \| Obligations of state and political subdivisions
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	24,694	13,027
Recurring fair value measurements \| Significant Other Observable Inputs (Level 2) \| Mortgage-backed securities
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	3,575	3,500
Recurring fair value measurements \| Significant Other Observable Inputs (Level 2) \| Corporate Securities
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	54,201	60,432
Recurring fair value measurements \| Significant Other Observable Inputs (Level 2) \| Equity Securities [Member]
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	5,104	5,795
Recurring fair value measurements \| Significant Unobservable Inputs (Level 3)
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	384	412
Recurring fair value measurements \| Significant Unobservable Inputs (Level 3) \| Equity Securities [Member]
Assets and Liabilities Measured at Fair Value
Investment securities available for sale	384	412
Nonrecurring Fair Value, Measurements
Assets and Liabilities Measured at Fair Value
Total nonrecurring fair value measurements	16,474	14,156
Nonrecurring Fair Value, Measurements \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets and Liabilities Measured at Fair Value
Total nonrecurring fair value measurements
Nonrecurring Fair Value, Measurements \| Significant Other Observable Inputs (Level 2)
Assets and Liabilities Measured at Fair Value
Total nonrecurring fair value measurements
Nonrecurring Fair Value, Measurements \| Significant Unobservable Inputs (Level 3)
Assets and Liabilities Measured at Fair Value
Total nonrecurring fair value measurements	16,474	14,156
Nonrecurring Fair Value, Measurements \| Significant Unobservable Inputs (Level 3) \| Collateral-dependent impaired loans
Assets and Liabilities Measured at Fair Value
Total nonrecurring fair value measurements	14,296	12,632
Nonrecurring Fair Value, Measurements \| Significant Unobservable Inputs (Level 3) \| Real Estate Loans
Assets and Liabilities Measured at Fair Value
Total nonrecurring fair value measurements	$ 2,178	$ 1,524

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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