Note 6 - Net Income Per Limited Partner Unit - Earning Per Unit (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Net income		$ 3,757
General partner interest in net income(loss)		105
Preferred interest in net income	6,279	6,279
Net loss available to limited partners	$ (6,279)	$ (2,627)
Common units (in shares)	41,015	40,678
Restricted and phantom units (in shares)	983	769
Total units (in shares)	41,998	41,447
Basic and diluted net loss per common unit (in dollars per share)	$ (0.15)	$ (0.06)