Premises and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 71,053	$ 72,316
Less accumulated depreciation	42,720	43,296
Total premises and equipment, net	28,333	29,020
Depreciation expense	3,500	3,700	$ 3,400
Land and Improvements [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	6,020	6,020
Premises and Improvements [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	38,793	37,913
Furniture, Fixtures and Equipment [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 26,240	$ 28,383