Note 10 - Stockholders' Equity - Non-vested Stock Options Activity (Details) - $ / shares	6 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Jun. 30, 2017
Outstanding, options (in shares)		1,156,027
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		2,233,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 2.36	$ 0.32	$ 2.16
Forfeited (in shares)		(338,518)
Outstanding, options (in shares)	1,156,027	3,023,639
Non-vested Stock Options [Member]
Outstanding, options (in shares)		835,708
Outstanding at January 1, 2018 (in dollars per share)		$ 2.37
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		2,233,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 0.32
Vested (in shares)		(651,180)
Vested (in dollars per share)		$ 0.97
Forfeited (in shares)		(296,131)
Forfeited (in dollars per share)		$ 2.35
Outstanding, options (in shares)	835,708	2,121,897
Outstanding at December 31, 2018 (in dollars per share)	$ 2.37	$ 0.64