Note 9 - Common Stock - Summary of Outstanding Warrants (Details) - $ / shares	9 Months Ended
	Sep. 30, 2019	May 22, 2017
Shares Outstanding Under Warrants (in shares)	5,549
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
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
Employee Performance Bonus Warrants, February 2015 Issuance [Member]
Expiration Date	Feb. 17, 2025
Exercise Price (in dollars per share)	$ 400
Shares Outstanding Under Warrants (in shares)	754
Contractor Warrants, March 2015 Issuance [Member]
Expiration Date	Mar. 26, 2025
Exercise Price (in dollars per share)	$ 272
Shares Outstanding Under Warrants (in shares)	14
Contractor Warrants, May 2015 Issuance [Member]
Expiration Date	May 12, 2025
Exercise Price (in dollars per share)	$ 424
Shares Outstanding Under Warrants (in shares)	362
May 2015 Issuance Second Contractor [Member]
Expiration Date	May 17, 2020
Exercise Price (in dollars per share)	$ 424
Shares Outstanding Under Warrants (in shares)	215
Performance Bonus Warrants, December 2015 Issuance [Member]
Expiration Date	Dec. 16, 2025
Exercise Price (in dollars per share)	$ 560
Shares Outstanding Under Warrants (in shares)	267
Distributor Warrants, April 2016 Issuance [Member]
Expiration Date	Apr. 01, 2026
Exercise Price (in dollars per share)	$ 608
Shares Outstanding Under Warrants (in shares)	250
Contractor Warrants, May 2016 Issuance [Member]
Expiration Date	May 11, 2021
Exercise Price (in dollars per share)	$ 774
Shares Outstanding Under Warrants (in shares)	50
June 2016 Issuance Related to 2016 Loan Agreement [Member]
Expiration Date	Jun. 20, 2026
Exercise Price (in dollars per share)	$ 498
Shares Outstanding Under Warrants (in shares)	1,004
May 2017 Issuance Related to 2017 Loan Agreement [Member]
Expiration Date	May 25, 2027
Exercise Price (in dollars per share)	$ 950	$ 950
Shares Outstanding Under Warrants (in shares)	2,220	2,220