Note 8 - Common Stock - Common Stock Reserved for Future Issuance (Details)	Dec. 31, 2018 shares
Common Stock, Reserved for Future Issuance (in shares)	265,565,942
Common Stock [Member]
Common Stock, Reserved for Future Issuance (in shares)	17,412,300
Warrant [Member]
Common Stock, Reserved for Future Issuance (in shares)	57,348,383
Series B Convertible Preferred Stock [Member]
Common Stock, Reserved for Future Issuance (in shares)	285,714
Series C Convertible Preferred Stock [Member]
Common Stock, Reserved for Future Issuance (in shares)	143,349,733
Series E Convertible Preferred Stock [Member]
Common Stock, Reserved for Future Issuance (in shares)	47,169,812