ORGANIZATION AND ACQUISITION OF THE NIAGRA GAMING BUNDLE - Additional Information (Details) $ in Thousands, $ in Thousands					3 Months Ended		6 Months Ended	9 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 11, 2019 CAD ($)	Jun. 11, 2019 USD ($)	Jun. 10, 2019 CAD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2019 seat	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Entity Information [Line Items]
Revenues					$ 347,607	$ 344,903		$ 974,804	$ 1,008,404
Capitalized contract cost, amortization period		21 years
Purchase price								72,287	$ 0
Long-term debt	$ 1,936,943				1,936,943			1,936,943		$ 1,814,155
MGE Niagara Credit Facility | Credit Facility
Entity Information [Line Items]
Long-term debt	75,140				75,140			75,140		0
MGE Niagara Credit Facility | Convertible Debenture
Entity Information [Line Items]
Long-term debt	30,476				30,476			30,476		$ 0
MG&E Niagra Entertainment
Entity Information [Line Items]
Number of seats (in seats) | seat							5,000
Operating lease, monthly payment	1,700	$ 2,200
Monthly payment under capital lease	381	500
Capital lease obligations	28,100	36,900			28,100			28,100
Intangible assets	5,300	6,900			5,300			5,300
Capitalized build-to-suit asset	78,400	102,900			78,400			78,400
Purchase price		96,000	$ 72,000
Cash acquired from acquisition		$ 57,000	$ 43,000
MG&E Niagra Entertainment | Credit Facility
Entity Information [Line Items]
Long-term debt	76,200			$ 100,000	76,200			76,200
MG&E Niagra Entertainment | Convertible Debenture
Entity Information [Line Items]
Long-term debt	30,500			40,000	$ 30,500			$ 30,500
MG&E Niagra Entertainment | MGE Niagara Credit Facility | Credit Facility
Entity Information [Line Items]
Equity method investment	$ 45,700			$ 60,000