Note 11 - Common Stock - Summary of Outstanding Warrants (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Nov. 30, 2019	Nov. 12, 2019	May 22, 2017
Shares Outstanding Under Warrants (in shares)	24,737,618	6,408
Employee Performance Bonus Warrants, February 2015 Issuance [Member]
Expiration Date	Feb. 17, 2025	Feb. 17, 2025
Exercise Price (in dollars per share)	$ 400	$ 400
Shares Outstanding Under Warrants (in shares)	754	754
September 2014 Issuance Through Private Offering [Member]
Expiration Date		Sep. 23, 2019
Exercise Price (in dollars per share)		$ 424
Shares Outstanding Under Warrants (in shares)		859
Contractor Warrants, March 2015 Issuance [Member]
Expiration Date	Mar. 26, 2025	Mar. 26, 2025
Exercise Price (in dollars per share)	$ 272	$ 272
Shares Outstanding Under Warrants (in shares)	14	14
Vendors and Contractor Warrants, October 2014 Issuance [Member]
Expiration Date		Oct. 13, 2019
Exercise Price (in dollars per share)		$ 424
Shares Outstanding Under Warrants (in shares)		288
Contractor Warrants, May 2015 Issuance [Member]
Expiration Date	May 12, 2025	May 12, 2025
Exercise Price (in dollars per share)	$ 424	$ 424
Shares Outstanding Under Warrants (in shares)	362	362
Vendors and Contractor Warrants, November 2014 Issuance [Member]
Expiration Date		Nov. 12, 2019
Exercise Price (in dollars per share)		$ 424
Shares Outstanding Under Warrants (in shares)		125
May 2015 Issuance Second Contractor [Member]
Expiration Date	May 17, 2020	May 17, 2020
Exercise Price (in dollars per share)	$ 424	$ 424
Shares Outstanding Under Warrants (in shares)	215	215
Performance Bonus Warrants, December 2015 Issuance [Member]
Expiration Date	Dec. 16, 2025	Dec. 16, 2025
Exercise Price (in dollars per share)	$ 560	$ 560
Shares Outstanding Under Warrants (in shares)	267	267
Distributor Warrants, April 2016 Issuance [Member]
Expiration Date	Apr. 01, 2026	Apr. 01, 2026
Exercise Price (in dollars per share)	$ 608	$ 608
Shares Outstanding Under Warrants (in shares)	250	250
Contractor Warrants, May 2016 Issuance [Member]
Expiration Date	May 11, 2021	May 11, 2021
Exercise Price (in dollars per share)	$ 774	$ 774
Shares Outstanding Under Warrants (in shares)	50	50
June 2016 Issuance Related to 2016 Loan Agreement [Member]
Expiration Date	Jun. 20, 2026	Jun. 20, 2026
Exercise Price (in dollars per share)	$ 498	$ 498
Shares Outstanding Under Warrants (in shares)	1,004	1,004
May 2017 Issuance Related to 2017 Loan Agreement [Member]
Expiration Date	May 25, 2027	May 25, 2027
Exercise Price (in dollars per share)	$ 950	$ 950			$ 950
Shares Outstanding Under Warrants (in shares)	2,220	2,220			2,220
Series A Warrants [Member]
Expiration Date	Nov. 26, 2020
Exercise Price (in dollars per share)	$ 1.55		$ 1.55
Shares Outstanding Under Warrants (in shares)	7,419,353		7,419,353
Series B Warrants [Member]
Expiration Date	Nov. 26, 2024
Exercise Price (in dollars per share)	$ 1.55		$ 1.55
Shares Outstanding Under Warrants (in shares)	7,419,353		7,419,353
Warrants Issued Upon Conversion of Term Loan with CRG [Member]
Expiration Date	Nov. 26, 2024
Exercise Price (in dollars per share)	$ 1.84
Shares Outstanding Under Warrants (in shares)	9,893,776			9,893,776