Fair value measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fair value measurements on a recurring basis \| Significant other observable inputs (Level 2) \| Bank
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale securities	$ 631,063	$ 624,331
Fair value measurements on a recurring basis \| Significant other observable inputs (Level 2) \| Other
Fair value measurements on a recurring and nonrecurring basis
Money market funds	10	10
Fair value measurements on a recurring basis \| Significant other observable inputs (Level 2) \| Mortgage-related securities - FNMA, FHLMC and GNMA \| Bank
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale securities	358,586	344,865
Fair value measurements on a recurring basis \| Significant other observable inputs (Level 2) \| Federal agency obligations \| Bank
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale securities	210,540	220,727
Fair value measurements on a recurring basis \| Significant other observable inputs (Level 2) \| Municipal bonds \| Bank
Fair value measurements on a recurring and nonrecurring basis
Available-for-sale securities	61,937	58,739
Fair value measurements on a nonrecurring basis \| Estimated fair value
Fair value measurements on a recurring and nonrecurring basis
Loans	33,000	34,000
Fair value measurements on a nonrecurring basis \| Significant Unobservable inputs (Level 3)
Fair value measurements on a recurring and nonrecurring basis
Loans	$ 33,000	$ 34,000

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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- Definition

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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