SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Non-Regulated Revenue
Maximum project completion period	3 months
Allowance for Doubtful Accounts
Activities in the allowance for doubtful accounts
Beginning Balance	$ 830	$ 730	$ 697
Provision for uncollectible accounts	1,570	2,111	1,674
Net write off of uncollectible accounts	(1,627)	(2,011)	(1,641)
Ending Balance	$ 773	$ 830	$ 730