Note 10 - Stockholders' Equity - Unvested Units Expected to Vest (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Unvested units expected to vest (in shares)	3,936,134	3,997,168
Share-based Payment Arrangement, Tranche One [Member]
Unvested units expected to vest (in shares)	1,988,079
Share-based Payment Arrangement, Tranche Two [Member]
Unvested units expected to vest (in shares)	1,428,145
Share-based Payment Arrangement, Tranche Three [Member]
Unvested units expected to vest (in shares)	519,910