Note 10 - Preferred Stock and Common Stock (Details Textual) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended
	Apr. 30, 2016	Feb. 28, 2015	Mar. 31, 2016	Dec. 31, 2015
ATM Program [Member] | Subsequent Event [Member]
Stock Issued During Period, Shares, New Issues	1,342,564
Proceeds from Issuance of Common Stock	$ 37.9
Payments of Stock Issuance Costs	$ 0.4
ATM Program [Member]
Common Stock, Par or Stated Value Per Share		$ 0.01
Maximum Aggregate Sales Price		$ 500.0
Stock Issued During Period, Shares, New Issues			3,618,831
Proceeds from Issuance of Common Stock			$ 100.6
Payments of Stock Issuance Costs			$ 1.0
Common Stock, Par or Stated Value Per Share			$ 0.01	$ 0.01