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Stock-Based Compensation Expense (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
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3 Months Ended |
9 Months Ended |
49 Months Ended |
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2014
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Dec. 31, 2013
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Jun. 30, 2014
plan
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Jul. 28, 2010
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Apr. 08, 2011
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| Stock-Based Compensation Expense |
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| Number of stock option award plans |
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2thr_NumberOfStockOptionAwardPlans
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| Options outstanding (in shares) |
475,895us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
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475,895us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
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| Stock compensation expense |
$ 930us-gaap_AllocatedShareBasedCompensationExpense
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$ 663us-gaap_AllocatedShareBasedCompensationExpense
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$ 2,302us-gaap_AllocatedShareBasedCompensationExpense
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$ 1,572us-gaap_AllocatedShareBasedCompensationExpense
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| Restricted Stock and Stock Option Plan |
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| Stock-Based Compensation Expense |
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| Maximum number of shares of the company's common stock that may be awarded |
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2,767,171us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= thr_RestrictedStockAndStockOptionPlanMember
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| 2011 Long-term Incentive Plan |
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| Stock-Based Compensation Expense |
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| Maximum number of shares of the company's common stock that may be awarded |
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2,893,341us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= thr_LongTermIncentivePlan2011Member
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| Restricted Stock Units |
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| Stock-Based Compensation Expense |
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| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period |
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93,562us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
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| Stock Issued During Period, Value, Restricted Stock Award, Gross |
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2,289us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
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| Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period |
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3 years
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| Common Stock [Member] |
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| Stock-Based Compensation Expense |
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| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period |
3,997us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_CommonStockMember
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7,945us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_CommonStockMember
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| Stock Issued During Period, Value, Restricted Stock Award, Gross |
96us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross
/ us-gaap_AwardTypeAxis
= us-gaap_CommonStockMember
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192us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross
/ us-gaap_AwardTypeAxis
= us-gaap_CommonStockMember
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| Share-based compensation arrangement by share-based payment award, fair value of shares authorized amount |
385thr_SharebasedCompensationArrangementbySharebasedPaymentAwardFairValueofSharesAuthorizedAmount
/ us-gaap_AwardTypeAxis
= us-gaap_CommonStockMember
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385thr_SharebasedCompensationArrangementbySharebasedPaymentAwardFairValueofSharesAuthorizedAmount
/ us-gaap_AwardTypeAxis
= us-gaap_CommonStockMember
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| Performance Shares [Member] |
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| Stock-Based Compensation Expense |
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| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period |
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46,530us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
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| Stock Issued During Period, Value, Restricted Stock Award, Gross |
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$ 1,189us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
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| Minimum |
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| Stock-Based Compensation Expense |
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| Share Price |
$ 24.07us-gaap_SharePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
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$ 24.07us-gaap_SharePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
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| Minimum | Performance Shares [Member] |
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| Stock-Based Compensation Expense |
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| Share-based compensation arrangement by share-based payment award, award requisite service period (in years) |
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2 years
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| Possible number of shares that could be issued (in shares) |
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0thr_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsPossibleNumberofPerformanceSharestobeGranted
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
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| Maximum |
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| Stock-Based Compensation Expense |
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| Share Price |
$ 25.89us-gaap_SharePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
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$ 25.89us-gaap_SharePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
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| Maximum | Performance Shares [Member] |
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| Stock-Based Compensation Expense |
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| Share-based compensation arrangement by share-based payment award, award requisite service period (in years) |
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3 years
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| Possible number of shares that could be issued (in shares) |
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93,060thr_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsPossibleNumberofPerformanceSharestobeGranted
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
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