Bank Premises and Equipment Depreciation Expense (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Bank Premises and Equipment
Depreciation expense	$ 3.0	$ 2.6	$ 2.2
Building and premises | Minimum
Bank Premises and Equipment
Building and premises and furniture, fixtures and equipment	5
Building and premises | Maximum
Bank Premises and Equipment
Building and premises and furniture, fixtures and equipment	40
Furniture, fixtures and equipment | Minimum
Bank Premises and Equipment
Building and premises and furniture, fixtures and equipment	2
Furniture, fixtures and equipment | Maximum
Bank Premises and Equipment
Building and premises and furniture, fixtures and equipment	10