Note 7 - Investments in Affordable Housing and Alternative Energy Partnerships (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Note 7 - Investments in Affordable Housing and Alternative Energy Partnerships (Details) [Line Items]
Affordable Housing Investments	$ 172.7	$ 104.6
Affordable Housing Investments, Net	$ 172.4	$ 104.6
Number of Limited Partnerships in Housing Investments	7	7
Increase in Total Assets and Liabilities from Consolidating Affordable Housing Equity Interest	$ 24.3	$ 24.8
Other Borrowings from Consolidating Affordable Housing Equity Interest	18.6	19.9
Other Liabilities from Affordable Housing Unfunded Commitments	$ 85.8	22.0
Minimum Compliance Period Tax Credits Investments in Affordable Housing	15 years
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount	$ 10.1	$ 10.2	$ 9.8
Alternative Energy Tax Credit Partnership Investments, Net	10.5
Energy Tax Credits Used, Amount	20.9
Domestic Tax Authority [Member] | Affordable Housing Limited Partnerships [Member]
Note 7 - Investments in Affordable Housing and Alternative Energy Partnerships (Details) [Line Items]
Remaining and Future Available Tax Credit	112.1
State and Local Jurisdiction [Member] | Affordable Housing Limited Partnerships [Member]
Note 7 - Investments in Affordable Housing and Alternative Energy Partnerships (Details) [Line Items]
Remaining and Future Available Tax Credit	$ 3.3