Premises and Equipment - Depreciation and Amortization Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 6,824	$ 6,251	$ 5,760
Premises
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	2,527	2,247	2,030
Furniture, fixtures, and equipment
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 4,297	$ 4,004	$ 3,730