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]
Property and equipment, gross	$ 130,004	$ 126,340
Less accumulated depreciation and amortization	(41,541)	(38,425)
Premises and equipment, net	88,463	87,915
Depreciation and amortization expense	4,400	5,000	$ 5,000
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	30,860	30,619
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	63,983	61,462
Furniture, fixtures, and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 35,161	$ 34,259