Premises and Equipment (Summary of Premises and Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Premises and Equipment
Premises and Equipment, gross amount	$ 151,113	$ 146,522
Accumulated depreciation and amortization	76,763	70,140
Total premises and equipment	74,350	76,382
Land
Premises and Equipment
Premises and Equipment, gross amount	12,320	12,300
Fine art
Premises and Equipment
Premises and Equipment, gross amount	545	533
Computer equipment
Premises and Equipment
Premises and Equipment, gross amount	$ 11,886	$ 10,488
Estimated useful life	3 years	3 years
Vehicles
Premises and Equipment
Premises and Equipment, gross amount	$ 135	$ 126
Core processing system and software
Premises and Equipment
Premises and Equipment, gross amount	20,748	20,466
Furniture, fixtures and equipment
Premises and Equipment
Premises and Equipment, gross amount	15,393	14,696
Office building and improvements
Premises and Equipment
Premises and Equipment, gross amount	$ 90,086	$ 87,913
Minimum | Vehicles
Premises and Equipment
Estimated useful life	3 years	3 years
Minimum | Core processing system and software
Premises and Equipment
Estimated useful life	3 years	3 years
Minimum | Furniture, fixtures and equipment
Premises and Equipment
Estimated useful life	5 years	5 years
Minimum | Office building and improvements
Premises and Equipment
Estimated useful life	10 years	10 years
Maximum | Vehicles
Premises and Equipment
Estimated useful life	5 years	5 years
Maximum | Core processing system and software
Premises and Equipment
Estimated useful life	7 years 6 months	7 years 6 months
Maximum | Furniture, fixtures and equipment
Premises and Equipment
Estimated useful life	25 years	25 years
Maximum | Office building and improvements
Premises and Equipment
Estimated useful life	40 years	40 years