Note 15 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Feb. 28, 2018
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
ATM Program [Member]
Common Stock, Par or Stated Value Per Share	$ 0.01
Sales of Stock Maximum Sales Price	$ 500.0
Share Repurchase Program [Member]
Common Stock, Par or Stated Value Per Share			$ 0.01
Stock Repurchase Program, Authorized Amount			$ 300.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 224.9