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Discontinued operations - Mexico project development- Narratives (Details)
$ / shares in Units, gal in Millions
 1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 29, 2020
Aug. 22, 2016
Feb. 28, 2018
Aug. 22, 2016
gal
Nov. 30, 2015
gal
Feb. 28, 2014
USD ($)
May 31, 2013
USD ($)
$ / shares
Feb. 29, 2012
USD ($)
May 31, 2010
gal
Jun. 30, 2020
USD ($)
Jun. 30, 2020
USD ($)
Dec. 31, 2015
gal
Sep. 30, 2020
USD ($)
ha
Dec. 31, 2018
Schedule of Investments [Line Items]                            
Land                         $ 21,100,000  
Period Required To Operate And Maintain Plant And Aqueduct   37 years                        
Subscription Agreement Description     The Agreement calls for NSC to retain a minimum of 25% of the equity in AdR. One or more affiliates of Greenfield SPV VII, S.A.P.I. de C.V. (“Greenfield”), a Mexico company managed by an affiliate of a leading U.S. asset manager, would acquire a minimum of 55% of the equity of AdR. The Agreement also provided Suez MA with the option to purchase 20% of the equity of AdR. If Suez MA did not exercise this option, NSC would retain 35% of the equity of AdR and Greenfield will acquire 65% of the equity of AdR. The Agreement became effective when the certain conditions precedent related to the Project were met. The aggregate investment to be made by the equity partners in the Project, in the form of equity and subordinated shareholder loans, is presently estimated at approximately 20% of the total cost of Phase 1 of the Project.                      
Number of days to submit list of non-recoverable expenses made 20 days                          
Impairment loss on long-lived assets                   $ (3,000,000.0)        
Adjustment to reduce operating lease right of use assets                   2,600,000 $ 2,600,000      
Adjustment to reduce operating lease liabilities                   $ 2,200,000 2,200,000      
Payments For Option Exercised           $ 1,000,000.0                
Share Price | $ / shares             $ 1              
Aguas de Rosarito S.A.P.I. de C.V [Member]                            
Schedule of Investments [Line Items]                            
Equity Method Investment, Ownership Percentage                         50.00%  
Option agreement [Member]                            
Schedule of Investments [Line Items]                            
Payments To Enter Option Agreement               $ 300,000            
NSC Agua [Member]                            
Schedule of Investments [Line Items]                            
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners                 50.00%          
Total Voting Interest Percentage After Conversion Of Loan                 99.99%          
Seawater Reverse Osmosis Desalination Plant Per Day Processing Capacity | gal       100         100          
Area of Land | ha                         20.1  
Equity Method Investment, Ownership Percentage                         50.00%  
Period in which construction must be completed   36 months                        
Payments for land and rights of way held for development                     $ 3,000,000.0      
Payments For Option Exercised           $ 1,000,000.0                
Percentage of Voting Interest Acquired through Option Agreement           25.00% 25.00%              
NSC Agua [Member] | Aguas de Rosarito S.A.P.I. de C.V [Member]                            
Schedule of Investments [Line Items]                            
Equity Method Investment, Ownership Percentage     0.40%                     99.60%
NSC Agua [Member] | First Phase [Member]                            
Schedule of Investments [Line Items]                            
Seawater Reverse Osmosis Desalination Plant Per Day Processing Capacity | gal       50 50             50    
NSC Agua [Member] | Second Phase [Member]                            
Schedule of Investments [Line Items]                            
Seawater Reverse Osmosis Desalination Plant Per Day Processing Capacity | gal       50 50             50    
NSC Agua [Member] | Option agreement [Member]                            
Schedule of Investments [Line Items]                            
Total Voting Interest Percentage After Conversion Of Loan             99.99%              
Repayment of inter-company loan payable             $ 5,700,000              
Option Agreement Expiration Date               Feb. 07, 2014