Note 2 - Recently Issued Accounting Standards (Details Textual) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017
Stock Options, Number of Shares with Exercise Prices Above the Closing Share Price	575,000
Expense from Expiration of Stock Options [Member] | Scenario, Forecast [Member]
Excess Tax Benefit from Share-based Compensation, Operating Activities		$ 2.7
Accounting Standards Update 2016-09 [Member]
Excess Tax Benefit from Share-based Compensation, Operating Activities	$ (0.1)