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Derivative Instruments (Details) - GOLDEN STATE WATER COMPANY
MWh in Thousands, $ in Thousands
3 Months Ended
Mar. 31, 2016
USD ($)
MWh
Mar. 31, 2015
USD ($)
Derivative Instruments, Gain (Loss) [Line Items]    
Description of derivative activity volume | MWh 457  
Commodity Contract    
Derivative Instruments, Gain (Loss) [Line Items]    
Number of broker quotes received to determine fair value of derivative instrument 1  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value at end of the period $ (7,053) $ (3,339)
Unrealized loss on purchased power contracts (192) (2,837)
Fair value at end of the period $ (7,245) $ (6,176)
Minimum | Commodity Contract    
Derivative Instruments, Gain (Loss) [Line Items]    
Term of derivative contract 3 years  
Maximum | Commodity Contract    
Derivative Instruments, Gain (Loss) [Line Items]    
Term of derivative contract 5 years