Note 16 - Stock-based Compensation - Share-based Compensation Award Activity (Details) - Board of Directors [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock With Exercise Price of $0.31 [Member] | Fourth Quarter of 2018 [Member]
Restricted Stock Exercise Price (in dollars per share)	$ 0.31
Restricted Stock Grants in Period (in shares)	50,808
Restricted Stock With Exercise Price of $0.25 [Member] | Third Quarter of 2018 [Member]
Restricted Stock Exercise Price (in dollars per share)	$ 0.25
Restricted Stock Grants in Period (in shares)	63,000
Restricted Stock with Exercise Price of $0.29 [Member] | Second Quarter of 2018 [Member]
Restricted Stock Exercise Price (in dollars per share)	$ 0.29
Restricted Stock Grants in Period (in shares)	54,308
Restricted Stock With Exercise Price of $0.24 [Member] | First Quarter of 2018 [Member]
Restricted Stock Exercise Price (in dollars per share)	$ 0.24
Restricted Stock Grants in Period (in shares)	65,624
Restricted Stock with Exercise Price of $0.28 [Member] | Fourth Quarter of 2017 [Member]
Restricted Stock Exercise Price (in dollars per share)		$ 0.28
Restricted Stock Grants in Period (in shares)		385,716
Restricted Stock with Exercise Price of $0.20 [Member] | Fourth Quarter of 2017 [Member]
Restricted Stock Exercise Price (in dollars per share)		$ 0.20
Restricted Stock Grants in Period (in shares)		78,752
Restricted Stock with Exercise Price of $0.20 [Member] | Third Quarter of 2017 [Member]
Restricted Stock Exercise Price (in dollars per share)		$ 0.20
Restricted Stock Grants in Period (in shares)		72,045
Restricted Stock with Exercise Price of $0.20 [Member] | First Quarter of 2017 [Member]
Restricted Stock Exercise Price (in dollars per share)		$ 0.20
Restricted Stock Grants in Period (in shares)		91,356
Second Issuance of Restricted Stock with Exercise Price of $0.21 [Member] | Second Quarter of 2017 [Member]
Restricted Stock Exercise Price (in dollars per share)		$ 0.21
Restricted Stock Grants in Period (in shares)		70,450
First Issuance of Restricted Stock with Exercise Price of $0.21 [Member] | Second Quarter of 2017 [Member]
Restricted Stock Exercise Price (in dollars per share)		$ 0.21
Restricted Stock Grants in Period (in shares)		55,833
Restricted Stock with Exercise Price of $0.15 [Member] | First Quarter of 2017 [Member]
Restricted Stock Exercise Price (in dollars per share)		$ 0.15
Restricted Stock Grants in Period (in shares)		210,000