| Stock Based Compensation (Details 4) (USD $) In Thousands, except Share data, unless otherwise specified | 12 Months Ended | |
|---|---|---|
| Dec. 31, 2014 | Dec. 31, 2013 | |
| Summary of stock based compensation agreements | ||
| Unrecognized stock-based compensation cost | $ 20,577us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized | $ 17,385us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized | 
| Weighted average years expense recognition period | 2 years 1 month 10 days | 2 years 2 months 5 days | 
| Total equity awards outstanding | 1,255,714mth_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesOutstanding | 1,317,710mth_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesOutstanding | 
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- Definition Share based compensation arrangement by share based payment award number of shares outstanding. No definition available. 
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- Details 
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- Definition Unrecognized cost of unvested share-based compensation awards. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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