Note 9 - Net Income Per Limited Partner Unit - Earning Per Unit (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019	Dec. 31, 2018
Net income (loss)	$ 4,340	$ 6,959	$ 3,356	$ 3,757	$ (50,682)	[1]	$ 2,408	[1]	$ 1,785	[1]	$ 4,442	[1]	$ 18,412	$ (42,047)	[1]
General partner interest in net income (loss)													337	(512)
Preferred interest in net income													25,115	25,115
Net loss available to limited partners													$ (7,040)	$ (66,650)
Common units (in shares)													40,755	40,348
Restricted and phantom units (in shares)													1,023	1,011
Total units (in shares)													41,778	41,359
Basic and diluted net loss per common unit (in dollars per share)	$ (0.05)	$ 0.01	$ (0.07)	$ (0.06)	$ (1.36)		$ (0.09)		$ (0.11)		$ (0.05)		$ (0.17)	$ (1.61)

[1] Operating loss and net loss for the fourth quarter and full year 2018 are impacted by asset impairment charges of $52.4 million and $53.1 million, respectively.