Bank Premises and Equipment Depreciation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Bank Premises and Equipment
Depreciation expense	$ 5.1	$ 4.6	$ 3.0
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