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Note 5 - Revenues (Details Textual)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Jun. 30, 2018
USD ($)
Sep. 30, 2014
Number of Suspended Saltwater Injection Wells             2
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 18,148 $ 16,364 $ 46,369 $ 41,643      
Membership Agreement, Term     1 year        
Allowance for Doubtful Accounts Receivable, Ending Balance 300   $ 300   $ 200    
Contract with Customer, Asset, Net, Total 774   774   580 $ 1,009  
Contract with Customer, Liability, Total 3,351   $ 3,351   $ 2,718 $ 4,034  
Accounts Receivable [Member] | Customer Concentration Risk [Member]              
Number of Major Customers     1   0    
Accounts Receivable [Member] | Customer Concentration Risk [Member] | One Customer [Member]              
Concentration Risk, Percentage     10.00%        
Waste Management Services [Member]              
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 12,557 $ 10,831 $ 32,525 $ 27,934      
Revenue from Contract with Customer, Excluding Assessed Tax, Percentage 69.00% 66.00% 70.00% 67.00%      
Waste Management Services [Member] | Accounts Receivable [Member] | Customer Concentration Risk [Member]              
Number of Major Customers     1        
Waste Management Services [Member] | Accounts Receivable [Member] | Customer Concentration Risk [Member] | One Customer [Member]              
Concentration Risk, Percentage     11.00%        
Waste Management Services [Member] | Maximum [Member]              
Contract Term     1 year        
Golf and Related Operations [Member]              
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 5,591 $ 5,533 $ 13,844 $ 13,709      
Revenue from Contract with Customer, Excluding Assessed Tax, Percentage 31.00% 34.00% 30.00% 33.00%      
Salt Water Injection Operations [Member] | Waste Management Services [Member]              
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 0 $ 0 $ 0 $ 0