Fair Value Measurements - Balances of assets and liabilities measured at fair value on recurring basis (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Assets:
Available-for-sale securities	$ 696,257	$ 691,563
Fair value, recurring basis | Estimate of fair value
Assets:
Available-for-sale securities	696,257	691,563
Loans held for sale	13,737	18,647
Mortgage banking derivatives	179	24
Total Assets	710,173	710,234
Liabilities:
Interest rate swap derivatives	2,973	2,013
Total Liabilities	2,973	2,013
Fair value, recurring basis | Estimate of fair value | Obligations of U.S. Government agencies
Assets:
Available-for-sale securities	103,042	145,976
Fair value, recurring basis | Estimate of fair value | Obligations of states and political subdivisions
Assets:
Available-for-sale securities	134,048	140,060
Fair value, recurring basis | Estimate of fair value | U.S. GSE's MBS - residential
Assets:
Available-for-sale securities	130,009	121,508
Fair value, recurring basis | Estimate of fair value | U.S. GSE's MBS - commercial
Assets:
Available-for-sale securities	29,382	21,669
Fair value, recurring basis | Estimate of fair value | U.S. GSE's CMO
Assets:
Available-for-sale securities	180,560	145,577
Fair value, recurring basis | Estimate of fair value | Corporate bonds
Assets:
Available-for-sale securities	119,216	116,773
Fair value, recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities
Loans held for sale
Mortgage banking derivatives
Total Assets
Liabilities:
Interest rate swap derivatives
Total Liabilities
Fair value, recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Obligations of U.S. Government agencies
Assets:
Available-for-sale securities
Fair value, recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Obligations of states and political subdivisions
Assets:
Available-for-sale securities
Fair value, recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. GSE's MBS - residential
Assets:
Available-for-sale securities
Fair value, recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. GSE's MBS - commercial
Assets:
Available-for-sale securities
Fair value, recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. GSE's CMO
Assets:
Available-for-sale securities
Fair value, recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Assets:
Available-for-sale securities
Fair value, recurring basis | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities	696,257	691,563
Loans held for sale	13,737	18,647
Mortgage banking derivatives	179	24
Total Assets	710,173	710,234
Liabilities:
Interest rate swap derivatives	2,973	2,013
Total Liabilities	2,973	2,013
Fair value, recurring basis | Significant Other Observable Inputs (Level 2) | Obligations of U.S. Government agencies
Assets:
Available-for-sale securities	103,042	145,976
Fair value, recurring basis | Significant Other Observable Inputs (Level 2) | Obligations of states and political subdivisions
Assets:
Available-for-sale securities	134,048	140,060
Fair value, recurring basis | Significant Other Observable Inputs (Level 2) | U.S. GSE's MBS - residential
Assets:
Available-for-sale securities	130,009	121,508
Fair value, recurring basis | Significant Other Observable Inputs (Level 2) | U.S. GSE's MBS - commercial
Assets:
Available-for-sale securities	29,382	21,669
Fair value, recurring basis | Significant Other Observable Inputs (Level 2) | U.S. GSE's CMO
Assets:
Available-for-sale securities	180,560	145,577
Fair value, recurring basis | Significant Other Observable Inputs (Level 2) | Corporate bonds
Assets:
Available-for-sale securities	119,216	116,773
Fair value, recurring basis | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities
Loans held for sale
Mortgage banking derivatives
Total Assets
Liabilities:
Interest rate swap derivatives
Total Liabilities
Fair value, recurring basis | Significant Unobservable Inputs (Level 3) | Obligations of U.S. Government agencies
Assets:
Available-for-sale securities
Fair value, recurring basis | Significant Unobservable Inputs (Level 3) | Obligations of states and political subdivisions
Assets:
Available-for-sale securities
Fair value, recurring basis | Significant Unobservable Inputs (Level 3) | U.S. GSE's MBS - residential
Assets:
Available-for-sale securities
Fair value, recurring basis | Significant Unobservable Inputs (Level 3) | U.S. GSE's MBS - commercial
Assets:
Available-for-sale securities
Fair value, recurring basis | Significant Unobservable Inputs (Level 3) | U.S. GSE's CMO
Assets:
Available-for-sale securities
Fair value, recurring basis | Significant Unobservable Inputs (Level 3) | Corporate bonds
Assets:
Available-for-sale securities