Investments in Affordable Housing Limit Partnerships (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Funding installments, term	2 years
Other non-interest expense
Schedule of Equity Method Investments [Line Items]
Expense related to investments in affordable housing limited partnerships	$ 1.5	$ 1.1	$ 1.5
Income tax expense
Schedule of Equity Method Investments [Line Items]
Affordable housing tax credits and other tax benefits recognized	1.4	1.4	$ 2.2
Other assets
Schedule of Equity Method Investments [Line Items]
Investment in affordable housing limited partnerships	15.7	17.2
Other liabilities
Schedule of Equity Method Investments [Line Items]
Funding obligation related to investments in affordable housing limited partnerships	$ 12.0	$ 12.9