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Note 5 - Revenues (Details Textual)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Sep. 03, 2014
Number of Suspended Saltwater Injection Wells 2       2
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 14,608 $ 11,516      
Membership Agreement, Term 1 year        
Accounts Receivable, Allowance for Credit Loss, Ending Balance $ 300   $ 300    
Contract with Customer, Asset, after Allowance for Credit Loss, Total 672 $ 694 554 $ 580  
Contract with Customer, Liability, Total $ 3,300   $ 2,900    
Customer Concentration Risk [Member] | Revenue Benchmark [Member]          
Number of Major Customers 0 0      
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Two Customers [Member]          
Concentration Risk, Percentage     23.00%    
Waste Management Services [Member]          
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 11,434 $ 8,458      
Revenue from Contract with Customer, Excluding Assessed Tax, Percentage 78.00% 73.00%      
Accounts Receivable, after Allowance for Credit Loss, Total $ 9,800   $ 11,200    
Waste Management Services [Member] | Maximum [Member]          
Contract Term 1 year        
Waste Management Services [Member] | Customer Concentration Risk [Member] | Revenue Benchmark [Member]          
Number of Major Customers 0 0      
Waste Management Services [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member]          
Number of Major Customers 0   2    
Waste Management Services [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member] | Two Customers [Member]          
Concentration Risk, Percentage     25.00%    
Golf and Related Operations [Member]          
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 3,174 $ 3,058      
Revenue from Contract with Customer, Excluding Assessed Tax, Percentage 22.00% 27.00%      
Number of Golf Courses 3        
Accounts Receivable, after Allowance for Credit Loss, Total $ 1,400   $ 1,000    
Golf and Related Operations [Member] | Customer Concentration Risk [Member] | Revenue Benchmark [Member]          
Number of Major Customers 0 0      
Golf and Related Operations [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member]          
Number of Major Customers 0   0    
Salt Water Injection Operations [Member] | Waste Management Services [Member]          
Revenue from Contract with Customer, Excluding Assessed Tax, Total $ 0 $ 0      
Customer Advance Deposits [Member]          
Contract with Customer, Liability, Total $ 536 $ 518 $ 453 $ 430