Note 10 - Developments in Accounting Pronouncements (Details Textual) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Equity Securities [Member]
Available-for-sale Securities, Accumulated Gross Unrealized Gain (Loss), before Tax	$ 3.2
Reclassification of Deferred Tax Assets from Current to Noncurrent [Member] | December 31, 2016 [Member]
Prior Period Reclassification Adjustment	12.3
Reclassification of Deferred Tax Liabilities from Current to Noncurrent [Member] | December 31, 2016 [Member]
Prior Period Reclassification Adjustment	$ 1.3