Note 3 - Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Total revenue	$ 27,759	$ 25,782	$ 54,834	$ 51,442
Third Party [Member]
Revenue from contracts with customers	7,312	6,835	14,231	13,688
Lease revenue	8,401	8,078	16,704	17,909
Related Party [Member]
Revenue from contracts with customers	5,035	4,041	9,884	8,096
Lease revenue	7,011	6,828	14,015	11,749
Fixed Storageand Throughput Revenue [Member]
Total revenue	9,804	8,001	19,588	16,004
Fixed Storageand Throughput Revenue [Member] | Third Party [Member]
Revenue from contracts with customers	5,084	5,110	10,147	10,222
Lease revenue	0	0	0	0
Fixed Storageand Throughput Revenue [Member] | Related Party [Member]
Revenue from contracts with customers	4,720	2,891	9,441	5,782
Lease revenue	0	0	0	0
Fixed Lease Revenue [Member]
Total revenue	14,607	14,048	29,192	28,075
Fixed Lease Revenue [Member] | Third Party [Member]
Revenue from contracts with customers	0	0	0	0
Lease revenue	7,821	7,487	15,621	16,713
Fixed Lease Revenue [Member] | Related Party [Member]
Revenue from contracts with customers	0	0	0	0
Lease revenue	6,786	6,561	13,571	11,362
Variable Cost Recovery Revenue [Member]
Total revenue	2,984	3,371	5,534	6,867
Variable Cost Recovery Revenue [Member] | Third Party [Member]
Revenue from contracts with customers	2,094	1,482	3,830	3,089
Lease revenue	465	472	968	1,077
Variable Cost Recovery Revenue [Member] | Related Party [Member]
Revenue from contracts with customers	200	1,150	292	2,314
Lease revenue	225	267	444	387
Variable Throughput Revenue [Member]
Total revenue	364	362	520	496
Variable Throughput Revenue [Member] | Third Party [Member]
Revenue from contracts with customers	134	243	254	377
Lease revenue	115	119	115	119
Variable Throughput Revenue [Member] | Related Party [Member]
Revenue from contracts with customers	115	0	151	0
Lease revenue	$ 0	$ 0	$ 0	$ 0