Note 9 - Stockholders' Equity - Unvested Units Expected to Vest (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Unvested units expected to vest (in shares)	3,997,168	2,689,468
Share-based Payment Arrangement, Tranche One [Member]
Unvested units expected to vest (in shares)	1,703,869
Share-based Payment Arrangement, Tranche Two [Member]
Unvested units expected to vest (in shares)	1,404,693
Share-based Payment Arrangement, Tranche Three [Member]
Unvested units expected to vest (in shares)	888,606