SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ASSETS HELD FOR SALE (Details) $ in Thousands		3 Months Ended
	Jun. 01, 2018 MW	Jun. 30, 2018 USD ($)
Assets Held For Sale Activity [Roll Forward]
Property, plant and equipment - wind equipment, at cost, ending balance		$ 3,199,057
Prepaid and accrued taxes, ending balance		47,017
Other noncurrent assets, ending balance		70,700
Assets held for sale, ending balance		206,898
Clean Energy Ventures
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Wind farm total capacity | MW	9.7
Clean Energy Ventures | Wind Assets And Related Liabilities
Assets Held For Sale Activity [Roll Forward]
Property, plant and equipment - wind equipment, at cost, beginning balance		244,972
Property, plant and equipment - accumulated depreciation, wind equipment, beginning balance		(21,561)
Prepaid and accrued taxes, beginning balance		1,226
Other noncurrent assets, beginning balance		261
Assets held for sale, beginning balance		224,898
Property, plant and equipment - wind equipment, at cost, assets sold		(20,688)
Property, plant and equipment - accumulated depreciation, wind equipment, assets sold		3,060
Prepaid and accrued taxes, assets sold		(77)
Other noncurrent assets, assets sold		0
Assets held for sale, assets sold		(17,705)
Prepaid and accrued taxes, other adjustments		(295)
Assets held for sale, other adjustments		(295)
Property, plant and equipment - wind equipment, at cost, ending balance		224,284
Property, plant and equipment - accumulated depreciation, wind equipment, ending balance		(18,501)
Prepaid and accrued taxes, ending balance		854
Other noncurrent assets, ending balance		261
Assets held for sale, ending balance		206,898
Accounts payable and other, beginning balance		0
Asset retirement obligation, beginning balance		4,262
Liabilities held for sale, beginning balance		4,262
Accounts payable and other, liabilities sold		186
Asset retirement obligation, liabilities sold		(266)
Liabilities held for sale, liabilities sold		80
Accounts payable and other, ending balance		186
Asset retirement obligation, ending balance		3,996
Liabilities held for sale, ending balance		$ 4,182