Premises and Equipment - Premises and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Premises and Equipment
Premises and equipment, gross	$ 21,032	$ 20,383
Accumulated depreciation and amortization	(13,679)	(12,893)
Premises and equipment, net	7,353	7,490
Building
Premises and Equipment
Premises and equipment, gross	3,508	3,400
Land
Premises and Equipment
Premises and equipment, gross	2,900	2,900
Furniture and equipment
Premises and Equipment
Premises and equipment, gross	9,256	8,788
Leasehold improvements
Premises and Equipment
Premises and equipment, gross	$ 5,368	$ 5,295