XML 41 R30.htm IDEA: XBRL DOCUMENT v3.8.0.1
Regulatory Assets and Liabilities (Details) - USD ($)
$ in Thousands
Jan. 01, 2018
Dec. 31, 2017
Dec. 31, 2016
Regulatory Assets [Line Items]      
Current regulatory assets   $ 4,707 $ 3,864
Noncurrent regulatory assets   22,747 34,900
Total regulatory assets   27,454 38,764
Regulatory Liabilities [Line Items]      
Regulatory liabilities   246,504 30,717
Total regulatory liabilities   248,043 32,183
Fuel recovery [Member]      
Regulatory Liabilities [Line Items]      
Current regulatory liabilities   1,539 1,466
Postretirement benefits [Member]      
Regulatory Liabilities [Line Items]      
Regulatory liabilities   34,089 30,587
Deferred Income Tax Charge [Member]      
Regulatory Liabilities [Line Items]      
Regulatory liabilities   206,547 0
Total regulatory liabilities $ 23,600    
Asset retirement obligations, net [Member]      
Regulatory Liabilities [Line Items]      
Regulatory liabilities   5,868 130
Levelized depreciation [Member]      
Regulatory Assets [Line Items]      
Current regulatory assets   4,707 3,864
Noncurrent regulatory assets   16,149 21,849
Deferred taxes on equity funds used during construction [Member]      
Regulatory Assets [Line Items]      
Noncurrent regulatory assets   $ 6,598 $ 13,051