Premises and Equipment, Net - Premises and Equipment Less Accumulated Depreciation and Amortization (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 66,899	$ 64,834
Accumulated depreciation and amortization	(41,153)	(37,924)
Premises and equipment, net	25,746	26,910
Land
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	4,018	4,018
Buildings and improvements
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	8,883	8,856
Capital leases
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	2,600	2,600
Furniture, fixtures, and equipment
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	22,677	21,962
Leasehold improvements
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 28,721	$ 27,398