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LONG-TERM DEBT (Details) (USD $)
3 Months Ended 33 Months Ended 12 Months Ended 1 Months Ended
Dec. 31, 2014
Sep. 18, 2014
Dec. 31, 2014
Oct. 31, 2014
Aug. 01, 2011
Dec. 05, 2014
Dec. 31, 2013
Long-term debt              
Long-term debt $ 610,827,000us-gaap_LongTermDebtNoncurrent   610,827,000us-gaap_LongTermDebtNoncurrent        
Loss on debt extinguishment 90,000us-gaap_GainsLossesOnExtinguishmentOfDebt 100,000us-gaap_GainsLossesOnExtinguishmentOfDebt          
2015              
Long-term debt              
Redemption price of debt instrument as a percentage of principal amount     106.00%us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodOneMember
       
2016              
Long-term debt              
Redemption price of debt instrument as a percentage of principal amount     103.00%us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodTwoMember
       
2017 and thereafter              
Long-term debt              
Redemption price of debt instrument as a percentage of principal amount     100.00%us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= us-gaap_DebtInstrumentRedemptionPeriodThreeMember
       
Minimum              
Long-term debt              
Consolidated debt ratio, requirement to purchase a portion of the outstanding notes     1.0mntg_DebtInstrumentCovenantConsolidatedDebtRatioRequirementForRedemptionOfNotes
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
       
Maximum              
Long-term debt              
Consolidated debt ratio, requirement to purchase a portion of the outstanding notes     4.0mntg_DebtInstrumentCovenantConsolidatedDebtRatioRequirementForRedemptionOfNotes
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
       
Senior Secured Second Lien Notes              
Long-term debt              
Long-term debt, gross 560,664,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
  560,664,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
       
Unamortized premium (discount) 50,163,000us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
  50,163,000us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
       
Debt issued         565,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
   
Interest rate (as a percent) 11.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
  11.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
       
Issue price as percentage of principal amount         97.00%mntg_LongTermDebtIssuePriceAsPercentageOfPrincipalAmount
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
   
Redemption price of debt instrument as a percentage of principal amount     100.00%us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
       
Principal amount of debt repurchased       10,000,000us-gaap_DebtInstrumentRepurchasedFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
     
Repurchase price (in dollars per share)       $ 110.25mntg_DebtInstrumentRepurchasePrice
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
     
Credit Facility              
Long-term debt              
Maximum borrowing capacity         20,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
   
Amount outstanding           0us-gaap_LineOfCredit
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_RevolvingCreditFacilityMember
 
Predecessor              
Long-term debt              
Long-term debt             558,834,000us-gaap_LongTermDebtNoncurrent
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
Predecessor | Senior Secured Second Lien Notes              
Long-term debt              
Long-term debt, gross             570,664,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
Unamortized premium (discount)             $ (11,830,000)us-gaap_DebtInstrumentUnamortizedDiscountPremiumNet
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
Interest rate (as a percent)             11.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= mntg_SeniorSecuredSecondLienNotes11.5PercentMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember