Bank Premises and Equipment - Summary of Bank Premises and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Cost	$ 121,919	$ 112,787
Accumulated Depreciation & Amortization	(50,895)	(45,904)
Net Carrying Value	71,024	66,883
Land	18,546	18,269
Premises
Property, Plant and Equipment [Line Items]
Cost	85,027	78,255
Accumulated Depreciation & Amortization	(26,107)	(24,045)
Net Carrying Value	58,920	54,210
Furniture and Equipment
Property, Plant and Equipment [Line Items]
Cost	36,892	34,532
Accumulated Depreciation & Amortization	(24,788)	(21,859)
Net Carrying Value	$ 12,104	$ 12,673