Note 6 - Stockholder's Equity (Details Textual) - $ / shares | Jun. 04, 2018 | Apr. 13, 2018 | Mar. 07, 2018 | Jan. 12, 2018 | Dec. 05, 2017 | Oct. 13, 2017 | Sep. 07, 2017 | Jul. 13, 2017 | Jun. 07, 2017 | May 22, 2017 | Apr. 20, 2017 | Mar. 15, 2017 | Aug. 18, 2015 | May 13, 2013 | May 06, 2013 | May 31, 2018 | May 31, 2017 | May 31, 2018 | May 31, 2017 |
Common Stock, Dividends, Per Share, Declared | | | | | | | | | | | | | | | | $ 0.01 | $ 0.01 | $ 0.03 | $ 0.03 |
Preferred Stock Dividends Number of Rights Declared | | | | | | | | | | | | | | | 1 | | | | |
Preferred Stock Dividends Number of Rights Issued | | | | | | | | | | | | | | 1 | | | | | |
Preferred Stock Dividends Number of Rights Minimum Percent of Common Stock that must be Acquired to Make Rights Exercisable | | | | | | | | | | | | | | | 15.00% | | | | |
Preferred Stock Dividends Number of Rights Minimum Percent of Common Stock that Must be Acquired to Make Rights Exercisable, Institutional Investors | | | | | | | | | | | | | | | 20.00% | | | | |
Right to Purchase Series A Preferred Stock [Member] | | | | | | | | | | | | | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right | | | | | | | | | | | | | | | 0.001 | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights | | | | | | | | | | | | | | | $ 0.90 | | | | |
Class of Warrant or Right, Term | | | | | | | | | | 7 years | | | 5 years | | 3 years | | | | |
Quarterly Dividend [Member] | | | | | | | | | | | | | | | | | | | |
Common Stock, Dividends, Per Share, Declared | | | $ 0.01 | | $ 0.01 | | $ 0.01 | | $ 0.01 | | | $ 0.01 | | | | | | | |
Common Stock, Dividends, Per Share, Cash Paid | | $ 0.01 | | $ 0.01 | | $ 0.01 | | $ 0.01 | | | $ 0.01 | | | | | | | | |
Dividends Payable, Date of Record | | | Mar. 27, 2018 | | | | | | | | | | | | | | | | |
Quarterly Dividend [Member] | Subsequent Event [Member] | | | | | | | | | | | | | | | | | | | |
Common Stock, Dividends, Per Share, Declared | $ 0.01 | | | | | | | | | | | | | | | | | | |
Dividends Payable, Date of Record | Jun. 19, 2018 | | | | | | | | | | | | | | | | | | |
Dividends Payable, Date to be Paid | Jul. 6, 2018 | | | | | | | | | | | | | | | | | | |
Special Cash Distribution [Member] | | | | | | | | | | | | | | | | | | | |
Common Stock, Dividends, Per Share, Declared | | | | | $ 0.01 | | | | | | | | | | | | | | |
Common Stock, Dividends, Per Share, Cash Paid | | | | $ 0.01 | | | | | | | | | | | | | | | |