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Note 5 - Revenues (Details Textual)
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Mar. 31, 2018
USD ($)
Sep. 30, 2014
Number of Suspended Saltwater Injection Wells             2
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 16,705 $ 14,577 $ 28,221 $ 25,279      
Membership Agreement, Term     1 year        
Allowance for Doubtful Accounts Receivable, Ending Balance 300   $ 300   $ 200    
Contract with Customer, Asset, Net, Total 1,009   1,009   580 $ 694  
Contract with Customer, Liability, Total 4,034   $ 4,034   $ 2,718 $ 3,147  
Accounts Receivable [Member] | Customer Concentration Risk [Member]              
Number of Major Customers     0   0    
Waste Management Services [Member]              
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 11,510 $ 9,490 $ 19,968 $ 17,103      
Revenue from Contract with Customer, Excluding Assessed Tax, Percentage 69.00% 65.00% 71.00% 68.00%      
Waste Management Services [Member] | Maximum [Member]              
Contract Term     1 year        
Golf and Related Operations [Member]              
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 5,195 $ 5,087 $ 8,253 $ 8,176      
Revenue from Contract with Customer, Excluding Assessed Tax, Percentage 31.00% 35.00% 29.00% 32.00%      
Salt Water Injection Operations [Member] | Waste Management Services [Member]              
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 0 $ 0