Disclosures about fair value of assets and liabilities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets
Total available for sale securities, Fair Value	$ 482,453	$ 482,801
Recurring basis [Member]
Assets
Total available for sale securities, Fair Value	482,453	482,801
Recurring basis [Member] | U.S. Treasury and federal agencies [Member]
Assets
Total available for sale securities, Fair Value	38,607	51,779
Recurring basis [Member] | State and municipal [Member]
Assets
Total available for sale securities, Fair Value	180,367	172,905
Recurring basis [Member] | Federal agency collateralized mortgage obligations [Member]
Assets
Total available for sale securities, Fair Value	108,803	96,831
Recurring basis [Member] | Federal agency mortgage-backed pools [Member]
Assets
Total available for sale securities, Fair Value	153,077	159,204
Recurring basis [Member] | Private labeled mortgage-backed pools [Member]
Assets
Total available for sale securities, Fair Value	1,554	2,031
Recurring basis [Member] | Corporate notes [Member]
Assets
Total available for sale securities, Fair Value	45	51
Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury and federal agencies [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | State and municipal [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Federal agency collateralized mortgage obligations [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Federal agency mortgage-backed pools [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Private labeled mortgage-backed pools [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate notes [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Total available for sale securities, Fair Value	482,453	482,801
Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury and federal agencies [Member]
Assets
Total available for sale securities, Fair Value	38,607	51,779
Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | State and municipal [Member]
Assets
Total available for sale securities, Fair Value	180,367	172,905
Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Federal agency collateralized mortgage obligations [Member]
Assets
Total available for sale securities, Fair Value	108,803	96,831
Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Federal agency mortgage-backed pools [Member]
Assets
Total available for sale securities, Fair Value	153,077	159,204
Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Private labeled mortgage-backed pools [Member]
Assets
Total available for sale securities, Fair Value	1,554	2,031
Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate notes [Member]
Assets
Total available for sale securities, Fair Value	45	51
Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury and federal agencies [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | State and municipal [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Federal agency collateralized mortgage obligations [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Federal agency mortgage-backed pools [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Private labeled mortgage-backed pools [Member]
Assets
Total available for sale securities, Fair Value
Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate notes [Member]
Assets
Total available for sale securities, Fair Value
Hedged loans [Member] | Recurring basis [Member]
Assets
Available-for-sale securities	83,545	81,018
Hedged loans [Member] | Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Available-for-sale securities
Hedged loans [Member] | Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Available-for-sale securities	83,545	81,018
Hedged loans [Member] | Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Available-for-sale securities
Forward sale commitments [Member] | Recurring basis [Member]
Assets
Available-for-sale securities	450	858
Forward sale commitments [Member] | Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Available-for-sale securities
Forward sale commitments [Member] | Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Available-for-sale securities	450	858
Forward sale commitments [Member] | Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Available-for-sale securities
Interest rate swap agreements [Member] | Recurring basis [Member]
Assets
Available-for-sale securities	(3,842)	(7,707)
Interest rate swap agreements [Member] | Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Available-for-sale securities
Interest rate swap agreements [Member] | Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Available-for-sale securities	(3,842)	(7,707)
Interest rate swap agreements [Member] | Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Available-for-sale securities
Commitments to originate loans [Member] | Recurring basis [Member]
Assets
Available-for-sale securities
Commitments to originate loans [Member] | Recurring basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Available-for-sale securities
Commitments to originate loans [Member] | Recurring basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Available-for-sale securities
Commitments to originate loans [Member] | Recurring basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Available-for-sale securities