SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Solar Asset Sale (Details) $ in Thousands	Jun. 30, 2018 USD ($)	Jun. 27, 2018 USD ($) site project MW	Dec. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Regulatory Assets	$ 476,635		$ 469,224
Disposal Group, Held-for-sale, Not Discontinued Operations | Marina
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of solar energy projects | project		76
Number of solar energy sites | site		143
Capacity of solar energy projects | MW		204
Consideration		$ 347,900
Ownership interest prior to disposal		100.00%
Potential aggregate downward adjustment		$ 5,400
Solar assets | Disposal Group, Held-for-sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Regulatory Assets	$ 428,900