Note 10 - Stockholders' Equity - Warrant Activity (Details) - $ / shares	6 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Jun. 30, 2017
Outstanding (in shares)	4,828,723	4,828,723	4,828,723
Outstanding, weighted average exercise price (in dollars per share)	$ 9.37	$ 9.37	$ 9.37
Warrants granted (in shares)		15,128,151
Warrants granted, weighted average exercise price (in dollars per share)		$ 0.42
Warrants exercised (in shares)		(2,691,666)
Warrants exercised, weighted average exercise price (in dollars per share)		$ 0.01
Warrants expired/canceled (in shares)
Warrants expired/canceled, weighted average exercise price (in dollars per share)
Outstanding (in shares)	4,828,723	17,265,208	4,828,723
Outstanding, weighted average exercise price (in dollars per share)	$ 9.37	$ 2.99	$ 9.37
Exercisable (in shares)	4,130,194	16,566,679	4,130,194
Exercisable, weighted average exercise price (in dollars per share)	$ 9.60	$ 2.78	$ 9.60