Note 6 - Net Income Per Limited Partner Unit - Earning Per Unit (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net income	$ 14,393	$ 6,959	$ 15,744	$ 14,072
General partner interest in net income	228	110	249	268
Preferred interest in net income	6,278	6,278	18,836	18,836
Net income (loss) available to limited partners	$ 7,887	$ 571	$ (3,341)	$ (5,032)
Common units (in shares)	41,166	40,811	41,072	40,735
Restricted and phantom units (in shares)	1,354	1,130	1,259	1,004
Total units (in shares)	42,520	41,941	42,331	41,739
Common units (in shares)	77,646	40,811	41,072	40,735
Basic net income (loss) per common unit (in dollars per share)	$ 0.19	$ 0.01	$ (0.08)	$ (0.12)
Diluted net income (loss) per common unit (in dollars per share)	$ 0.18	$ 0.01	$ (0.08)	$ (0.12)