Fair Value of Financial Instruments Recurring basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments
Total held-to-maturity securities	$ 41,213	$ 43,227
Total available-for-sale securities	795,187	777,940
Recurring Basis
Investments
Total available-for-sale securities	795,187	777,940
U.S. government sponsored agencies
Investments
Total available-for-sale securities		1,000
U.S. government sponsored agencies | Recurring Basis
Investments
Total available-for-sale securities		1,000
States and political subdivisions
Investments
Total held-to-maturity securities	4,417	4,041
Total available-for-sale securities	101,569	117,230
States and political subdivisions | Recurring Basis
Investments
Total available-for-sale securities	101,569	117,230
Residential mortgage-backed securities
Investments
Total held-to-maturity securities	32,227	33,762
Total available-for-sale securities	673,664	626,567
Residential mortgage-backed securities | Recurring Basis
Investments
Total available-for-sale securities	673,664	626,567
Commercial mortgage-backed securities
Investments
Total held-to-maturity securities	4,569	5,424
Total available-for-sale securities	6,976	19,291
Commercial mortgage-backed securities | Recurring Basis
Investments
Total available-for-sale securities	6,976	19,291
Bank-issued trust preferred securities
Investments
Total available-for-sale securities	5,129	4,899
Bank-issued trust preferred securities | Recurring Basis
Investments
Total available-for-sale securities	5,129	4,899
Equity securities
Investments
Total available-for-sale securities	7,849	8,953
Equity securities | Recurring Basis
Investments
Total available-for-sale securities	7,849	8,953
Quoted Prices in Active Markets for Identical Assets (Level 1)
Investments
Total held-to-maturity securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring Basis
Investments
Total available-for-sale securities	7,694	8,734
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. government sponsored agencies | Recurring Basis
Investments
Total available-for-sale securities		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | States and political subdivisions
Investments
Total held-to-maturity securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | States and political subdivisions | Recurring Basis
Investments
Total available-for-sale securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential mortgage-backed securities
Investments
Total held-to-maturity securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential mortgage-backed securities | Recurring Basis
Investments
Total available-for-sale securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial mortgage-backed securities
Investments
Total held-to-maturity securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial mortgage-backed securities | Recurring Basis
Investments
Total available-for-sale securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Bank-issued trust preferred securities | Recurring Basis
Investments
Total available-for-sale securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities | Recurring Basis
Investments
Total available-for-sale securities	7,694	8,734
Significant Other Observable Inputs (Level 2)
Investments
Total held-to-maturity securities	41,213	43,227
Significant Other Observable Inputs (Level 2) | Recurring Basis
Investments
Total available-for-sale securities	787,493	769,206
Significant Other Observable Inputs (Level 2) | U.S. government sponsored agencies | Recurring Basis
Investments
Total available-for-sale securities		1,000
Significant Other Observable Inputs (Level 2) | States and political subdivisions
Investments
Total held-to-maturity securities	4,417	4,041
Significant Other Observable Inputs (Level 2) | States and political subdivisions | Recurring Basis
Investments
Total available-for-sale securities	101,569	117,230
Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities
Investments
Total held-to-maturity securities	32,227	33,762
Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities | Recurring Basis
Investments
Total available-for-sale securities	673,664	626,567
Significant Other Observable Inputs (Level 2) | Commercial mortgage-backed securities
Investments
Total held-to-maturity securities	4,569	5,424
Significant Other Observable Inputs (Level 2) | Commercial mortgage-backed securities | Recurring Basis
Investments
Total available-for-sale securities	6,976	19,291
Significant Other Observable Inputs (Level 2) | Bank-issued trust preferred securities | Recurring Basis
Investments
Total available-for-sale securities	5,129	4,899
Significant Other Observable Inputs (Level 2) | Equity securities | Recurring Basis
Investments
Total available-for-sale securities	155	219
Significant Unobservable Inputs (Level 3)
Investments
Total held-to-maturity securities	0	0
Significant Unobservable Inputs (Level 3) | Recurring Basis
Investments
Total available-for-sale securities	0	0
Significant Unobservable Inputs (Level 3) | U.S. government sponsored agencies | Recurring Basis
Investments
Total available-for-sale securities		0
Significant Unobservable Inputs (Level 3) | States and political subdivisions
Investments
Total held-to-maturity securities	0	0
Significant Unobservable Inputs (Level 3) | States and political subdivisions | Recurring Basis
Investments
Total available-for-sale securities	0	0
Significant Unobservable Inputs (Level 3) | Residential mortgage-backed securities
Investments
Total held-to-maturity securities	0	0
Significant Unobservable Inputs (Level 3) | Residential mortgage-backed securities | Recurring Basis
Investments
Total available-for-sale securities	0	0
Significant Unobservable Inputs (Level 3) | Commercial mortgage-backed securities
Investments
Total held-to-maturity securities	0	0
Significant Unobservable Inputs (Level 3) | Commercial mortgage-backed securities | Recurring Basis
Investments
Total available-for-sale securities	0	0
Significant Unobservable Inputs (Level 3) | Bank-issued trust preferred securities | Recurring Basis
Investments
Total available-for-sale securities	0	0
Significant Unobservable Inputs (Level 3) | Equity securities | Recurring Basis
Investments
Total available-for-sale securities	$ 0	$ 0