Note 8 - Fair Value - Fair Value of Equity Securities (Details)	6 Months Ended
	Jun. 30, 2018 $ / shares
Series B-3 Cumulative Convertible Preferred Stock [Member]
Estimated fair value per share (in dollars per share)	$ 4.12
Series A Preferred Stock [Member]
Estimated fair value per share (in dollars per share)	1,000
Series B Preferred Stock [Member]
Estimated fair value per share (in dollars per share)	$ 1.52