Annual report pursuant to Section 13 and 15(d)

Stock Based Compensation (Details)

v2.4.1.9
Stock Based Compensation (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Options      
Options outstanding at beginning of year (shares) 258,815us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 609,585us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 897,767us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Granted (shares) 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Exercised (shares) (60,695)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised (347,370)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised (282,082)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
Cancelled (shares) (16,680)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod (3,400)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod (6,100)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
Outstanding at end of year (shares) 181,440us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 258,815us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 609,585us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Weighted Average Exercise Price      
Options outstanding at beginning of year (shares) $ 19.63us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 27.44us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 23.56us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Exercised (shares) $ 17.16us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice $ 33.40us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice $ 15.12us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
Cancelled (shares) $ 38.86us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice $ 14.00us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice $ 25.73us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice
Outstanding at end of year (shares) $ 18.69us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 19.63us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 27.44us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Options outstanding at end of year, additional disclosures      
Weighted Average Remaining Contractual Life 5 months 7 days    
Aggregate Intrinsic Value $ 3,139us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue    
Vested at end of year      
Vested and expected to vest at end of year (shares) 181,440us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber    
Weighted Average Exercise Price (shares) $ 18.69us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice    
Weighted Average Remaining Contractual Life 5 months 7 days    
Aggregate Intrinsic Value 3,139us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue    
Exercisable at end of year      
Options (shares) 181,440us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber 225,415us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber 471,760us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
Weighted Average Exercise Price (shares) $ 18.69us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice $ 20.36us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice $ 30.93us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice
Weighted Average Remaining Contractual Life 5 months 7 days    
Aggregate Intrinsic Value $ 3,139us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1    
Price range of options exercised - lower range limit $ 11.48mth_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOfOptionsExercisedLowerRange $ 8.06mth_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOfOptionsExercisedLowerRange $ 8.06mth_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOfOptionsExercisedLowerRange
Price range of options exercised - upper range limit $ 42.82mth_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOfOptionsExercisedUpperRange $ 44.44mth_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOfOptionsExercisedUpperRange $ 34.30mth_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOfOptionsExercisedUpperRange
Price range of options outstanding - lower range limit $ 11.48us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit $ 11.48us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit $ 8.06us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
Price range of options outstanding - upper range limit $ 22.11us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit $ 42.82us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit $ 44.44us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
Total shares reserved for existing or future equity award grants at end of year 2,885,481us-gaap_CommonStockCapitalSharesReservedForFutureIssuance