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Leases (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
Trust
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 1986
Trust
Estimated future minimum lease payments for operating leases, excluding purchased power agreements        
Lease expense $ 18,000 $ 16,000 $ 17,000  
Pinnacle West        
Estimated future minimum lease payments for operating leases, excluding purchased power agreements        
2018 13,412      
2019 11,054      
2020 9,641      
2021 7,105      
2022 4,609      
Thereafter 55,940      
Total future lease commitments 101,761      
Palo Verde Lessor Trusts        
Estimated future minimum lease payments for operating leases, excluding purchased power agreements        
Number of VIE lessor trusts | Trust       3
APS        
Estimated future minimum lease payments for operating leases, excluding purchased power agreements        
2018 13,110      
2019 10,802      
2020 9,392      
2021 6,858      
2022 4,510      
Thereafter 53,605      
Total future lease commitments 98,277      
Lease expense $ 17,000 $ 15,000 $ 14,000  
Number of VIE lessor trusts | Trust 3     3