LEASES - Cost and Accumulated Depreciation (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Leases [Abstract]
Property and equipment, at cost	$ 492,612
Less: accumulated depreciation	(197,212)
Total	$ 295,400

Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, before Accumulated Depreciation and Amortization

No definition available.

Name:	mtga_PropertyPlantandEquipmentandFinanceLeaseRightofUseAssetbeforeAccumulatedDepreciationandAmortization
Namespace Prefix:	mtga_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant