OTHER DEFERRED CREDITS AND OTHER LIABILITIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Deferred credits and other liabilities
Transmission easements	$ 21,337	$ 21,337
Contract liabilities (unearned revenue) - noncurrent	6,560	6,673
Customer deposits	2,690	2,898
Other	21,688	22,488
Total other deferred credits and other liabilities	52,275	53,396
Transmission Right of Way Easements
Deferred credits and other liabilities
Total due for easement right of way	34,500
Other Deferred Credits and Other Liabilities | Transmission Right of Way Easements
Deferred credits and other liabilities
Transmission easements	$ 21,300	$ 21,300