Note 8 - Stockholders' Equity - Warrants Outstanding by Exercise Price (Details) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Exercise prices of warrants (in dollars per share)	$ 6.60	$ 6.60
Warrants outstanding (in shares)	100,000
Warrants outstanding, weighted average remaining contractual life (Year)	116 days
Warrants outstanding, weighted average exercise price (in dollars per share)	$ 6.60
Warrants exercisable (in shares)	100,000
Warrants exercisable, weighted average exercise price (in dollars per share)	$ 6.60
Warrant 1 [Member]
Exercise prices of warrants (in dollars per share)	$ 6.60
Warrants outstanding (in shares)	100,000
Warrants outstanding, weighted average remaining contractual life (Year)	116 days
Warrants outstanding, weighted average exercise price (in dollars per share)	$ 6.60
Warrants exercisable (in shares)	100,000
Warrants exercisable, weighted average exercise price (in dollars per share)	$ 6.60