NEW ACCOUNTING STANDARDS - Income Statement Impacts (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Gross revenues	$ 1,388,810	$ 1,388,810	$ 1,456,980	$ 1,485,350
Less-Promotional allowances	0	0	(101,348)	(105,347)
Net revenues	1,388,810	1,388,810	1,355,632	1,380,003
Operating costs and expenses:
Advertising, general and administrative	223,716	223,716	200,786	203,922
Corporate	45,880	45,880	40,087	44,749
Depreciation and amortization	122,657	122,657	81,789	74,443
Impairment of Mohegan Sun Pocono's goodwill	39,459	39,459	0	0
Other, net	9,273	9,273	13,220	2,230
Total operating costs and expenses	1,252,348	1,252,348	1,111,098	1,122,768
Income from operations	136,462	136,462	244,534	257,235
Balance without Adoption of ASC 606
Revenues:
Gross revenues	1,522,448
Less-Promotional allowances	(123,157)
Net revenues	1,399,291
Operating costs and expenses:
Advertising, general and administrative	223,225
Corporate	45,880
Depreciation and amortization	122,657
Impairment of Mohegan Sun Pocono's goodwill	39,459
Other, net	9,273
Total operating costs and expenses	1,265,964
Income from operations	133,327
Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	(133,638)
Less-Promotional allowances	123,157
Net revenues	(10,481)
Operating costs and expenses:
Advertising, general and administrative	491
Corporate	0
Depreciation and amortization	0
Impairment of Mohegan Sun Pocono's goodwill	0
Other, net	0
Total operating costs and expenses	(13,616)
Income from operations	3,135
Gaming
Revenues:
Gross revenues	936,412	936,412	1,162,300	1,179,865
Operating costs and expenses:
Cost of goods sold	551,738	551,738	655,956	670,692
Gaming | Balance without Adoption of ASC 606
Revenues:
Gross revenues	1,160,475
Operating costs and expenses:
Cost of goods sold	690,438
Gaming | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	(224,063)
Operating costs and expenses:
Cost of goods sold	(138,700)
Food and beverage
Revenues:
Gross revenues	157,544	157,544	88,247	90,310
Operating costs and expenses:
Cost of goods sold	123,814	123,814	41,102	41,041
Food and beverage | Balance without Adoption of ASC 606
Revenues:
Gross revenues	111,810
Operating costs and expenses:
Cost of goods sold	51,542
Food and beverage | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	45,734
Operating costs and expenses:
Cost of goods sold	72,272
Hotel
Revenues:
Gross revenues	97,235	97,235	62,378	63,518
Operating costs and expenses:
Cost of goods sold	42,476	42,476	27,756	27,713
Hotel | Balance without Adoption of ASC 606
Revenues:
Gross revenues	72,165
Operating costs and expenses:
Cost of goods sold	29,702
Hotel | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	25,070
Operating costs and expenses:
Cost of goods sold	12,774
Retail, entertainment, and other
Revenues:
Gross revenues	197,619	197,619	144,055	151,657
Operating costs and expenses:
Cost of goods sold	93,335	$ 93,335	$ 50,402	$ 57,978
Retail, entertainment, and other | Balance without Adoption of ASC 606
Revenues:
Gross revenues	177,998
Operating costs and expenses:
Cost of goods sold	53,788
Retail, entertainment, and other | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	19,621
Operating costs and expenses:
Cost of goods sold	39,547
Loyalty Points | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	2,688
Less-Promotional allowances	0
Net revenues	2,688
Operating costs and expenses:
Advertising, general and administrative	0
Corporate	0
Depreciation and amortization	0
Impairment of Mohegan Sun Pocono's goodwill	0
Other, net	0
Total operating costs and expenses	(447)
Income from operations	3,135
Loyalty Points | Gaming | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	2,688
Operating costs and expenses:
Cost of goods sold	(447)
Loyalty Points | Food and beverage | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	0
Operating costs and expenses:
Cost of goods sold	0
Loyalty Points | Hotel | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	0
Operating costs and expenses:
Cost of goods sold	0
Loyalty Points | Retail, entertainment, and other | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	0
Operating costs and expenses:
Cost of goods sold	0
Promotional Allowances (Discretionary Complementaries) | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	(92,295)
Less-Promotional allowances	97,343
Net revenues	5,048
Operating costs and expenses:
Advertising, general and administrative	0
Corporate	0
Depreciation and amortization	0
Impairment of Mohegan Sun Pocono's goodwill	0
Other, net	0
Total operating costs and expenses	5,048
Income from operations	0
Promotional Allowances (Discretionary Complementaries) | Gaming | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	(178,234)
Operating costs and expenses:
Cost of goods sold	(21,730)
Promotional Allowances (Discretionary Complementaries) | Food and beverage | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	41,758
Operating costs and expenses:
Cost of goods sold	26,467
Promotional Allowances (Discretionary Complementaries) | Hotel | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	24,394
Operating costs and expenses:
Cost of goods sold	0
Promotional Allowances (Discretionary Complementaries) | Retail, entertainment, and other | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	19,787
Operating costs and expenses:
Cost of goods sold	311
Promotional Allowances (Non-Discretionary Complementaries) | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	(57,059)
Less-Promotional allowances	23,505
Net revenues	(33,554)
Operating costs and expenses:
Advertising, general and administrative	0
Corporate	0
Depreciation and amortization	0
Impairment of Mohegan Sun Pocono's goodwill	0
Other, net	0
Total operating costs and expenses	(33,554)
Income from operations	0
Promotional Allowances (Non-Discretionary Complementaries) | Gaming | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	(62,678)
Operating costs and expenses:
Cost of goods sold	(131,384)
Promotional Allowances (Non-Discretionary Complementaries) | Food and beverage | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	0
Operating costs and expenses:
Cost of goods sold	41,879
Promotional Allowances (Non-Discretionary Complementaries) | Hotel | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	0
Operating costs and expenses:
Cost of goods sold	12,099
Promotional Allowances (Non-Discretionary Complementaries) | Retail, entertainment, and other | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	5,619
Operating costs and expenses:
Cost of goods sold	43,852
Cash Promotions | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	(7,683)
Less-Promotional allowances	0
Net revenues	(7,683)
Operating costs and expenses:
Advertising, general and administrative	0
Corporate	0
Depreciation and amortization	0
Impairment of Mohegan Sun Pocono's goodwill	0
Other, net	0
Total operating costs and expenses	(7,683)
Income from operations	0
Cash Promotions | Gaming | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	(7,683)
Operating costs and expenses:
Cost of goods sold	(7,683)
Cash Promotions | Food and beverage | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	0
Operating costs and expenses:
Cost of goods sold	0
Cash Promotions | Hotel | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	0
Operating costs and expenses:
Cost of goods sold	0
Cash Promotions | Retail, entertainment, and other | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	0
Operating costs and expenses:
Cost of goods sold	0
Gross vs. Net Presentation and Other | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	20,711
Less-Promotional allowances	2,309
Net revenues	23,020
Operating costs and expenses:
Advertising, general and administrative	491
Corporate	0
Depreciation and amortization	0
Impairment of Mohegan Sun Pocono's goodwill	0
Other, net	0
Total operating costs and expenses	23,020
Income from operations	0
Gross vs. Net Presentation and Other | Gaming | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	21,844
Operating costs and expenses:
Cost of goods sold	22,544
Gross vs. Net Presentation and Other | Food and beverage | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	3,976
Operating costs and expenses:
Cost of goods sold	3,926
Gross vs. Net Presentation and Other | Hotel | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	676
Operating costs and expenses:
Cost of goods sold	675
Gross vs. Net Presentation and Other | Retail, entertainment, and other | Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Revenues:
Gross revenues	(5,785)
Operating costs and expenses:
Cost of goods sold	$ (4,616)