Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair value measurement
Securities available-for-sale	$ 785,693	$ 814,931
US Government Agencies Debt Securities [Member]
Fair value measurement
Securities available-for-sale	12,473	13,695
Mortgage Backed Securities - Residential
Fair value measurement
Securities available-for-sale	184,651	215,338
Mortgage Backed Securities - Commercial
Fair value measurement
Securities available-for-sale		1
Collateralized Mortgage Obligations
Fair value measurement
Securities available-for-sale	354,547	339,670
State and Municipal Obligations
Fair value measurement
Securities available-for-sale	230,599	231,622
Collateralized Debt Obligations
Fair value measurement
Securities available-for-sale	3,423	14,605
Fair Value, Inputs, Level 1 [Member]
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities [Member]
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 1 [Member] | Mortgage Backed Securities - Residential
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 1 [Member] | Mortgage Backed Securities - Commercial
Fair value measurement
Securities available-for-sale		0
Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Obligations
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 1 [Member] | State and Municipal Obligations
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 1 [Member] | Collateralized Debt Obligations
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 2 [Member]
Fair value measurement
Securities available-for-sale	779,135	796,646
Derivative Assets	687	298
Derivative Liability	(687)	(298)
Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member]
Fair value measurement
Securities available-for-sale	12,473	13,695
Fair Value, Inputs, Level 2 [Member] | Mortgage Backed Securities - Residential
Fair value measurement
Securities available-for-sale	184,651	215,338
Fair Value, Inputs, Level 2 [Member] | Mortgage Backed Securities - Commercial
Fair value measurement
Securities available-for-sale		1
Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Obligations
Fair value measurement
Securities available-for-sale	354,547	339,670
Fair Value, Inputs, Level 2 [Member] | State and Municipal Obligations
Fair value measurement
Securities available-for-sale	227,464	227,942
Fair Value, Inputs, Level 2 [Member] | Collateralized Debt Obligations
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 3 [Member]
Fair value measurement
Securities available-for-sale	6,558	18,285
Fair Value, Inputs, Level 3 [Member] | US Government Agencies Debt Securities [Member]
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 3 [Member] | Mortgage Backed Securities - Residential
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 3 [Member] | Mortgage Backed Securities - Commercial
Fair value measurement
Securities available-for-sale		0
Fair Value, Inputs, Level 3 [Member] | Collateralized Mortgage Obligations
Fair value measurement
Securities available-for-sale	0	0
Fair Value, Inputs, Level 3 [Member] | State and Municipal Obligations
Fair value measurement
Securities available-for-sale	3,135	3,680
Fair Value, Inputs, Level 3 [Member] | Collateralized Debt Obligations
Fair value measurement
Securities available-for-sale	$ 3,423	$ 14,605