VARIABLE INTEREST ENTITIES - Summary of the Carrying Value of the Assets and Liabilities and Maximum Loss Exposure for the Alternative Energy Partnerships (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash	$ 16,518	$ 0
Equipment, net of depreciation	246,297	151,721
Other assets	2,444	351
Total unconsolidated assets	265,259	152,072
Total unconsolidated liabilities	7,181	0
Maximum loss exposure	$ 98,910	$ 68,298

VARIABLE INTEREST ENTITIES - Summary of the Carrying Value of the Assets and Liabilities and Maximum Loss Exposure for the Alternative Energy Partnerships (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($)
$ in Thousands

Dec. 31, 2017

Dec. 31, 2016

Variable Interest Entity [Line Items]

Cash

$ 16,518

$ 0

Equipment, net of depreciation

246,297

151,721

Other assets

2,444

351