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Goodwill and Intangible Assets (Details 2) (USD $) | 6 Months Ended |
--- | --- | ---
Mar. 29, 2015 | Sep. 28, 2014
Goodwill | 671,397,000 us-gaap_Goodwill | $ 714,190,000 us-gaap_Goodwill
RME |  |
Goodwill | 448,839,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember | 476,104,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember
RME | GMP |  |
Fair value of business | 102,800,000 us-gaap_FairValueNetAssetLiability / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
Carrying value of business | 91,800,000 us-gaap_AssetsNet / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
Goodwill | 61,400,000 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
RME | GMP | US treasury bonds |  |
Impairment of goodwill |  |
Maturity of investments whose yield is considered in determination of impairment | 20 years |
Goodwill. | RME | GMP |  |
Discounted cash flow rate (as a percent) | 14.00%us-gaap_FairValueInputsDiscountRate / us-gaap_FairValueByAssetClassAxis = us-gaap_GoodwillMember / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
Revenue multiple | 0.7 us-gaap_FairValueInputsRevenueMultiple / us-gaap_FairValueByAssetClassAxis = us-gaap_GoodwillMember / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
Impairment of goodwill |  |
Significant contraction in mining activity period | 2 years |
Goodwill. | RME | GMP | Minimum |  |
Annual revenue growth rate (as a percent) | 3.00%us-gaap_FairValueInputsLongTermRevenueGrowthRate / us-gaap_FairValueByAssetClassAxis = us-gaap_GoodwillMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
Impairment of goodwill |  |
Decline in future revenue leading to goodwill impairment (as a percent) | 20.00%ttek_GoodwillDecreaseInRevenueThatWouldLeadToImpairment / us-gaap_FairValueByAssetClassAxis = us-gaap_GoodwillMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
Decline in future market prices of similar businesses leading to goodwill impairment (as a percent) | 15.00%ttek_GoodwillDecreaseInMarketPricesForSimilarBusinessesThatWouldLeadToImpairment / us-gaap_FairValueByAssetClassAxis = us-gaap_GoodwillMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
Discounted cash flow rate leading to impairment of goodwill (as a percent) | 15.50%ttek_GoodwillDiscountedCashFlowThatWouldLeadToImpairment / us-gaap_FairValueByAssetClassAxis = us-gaap_GoodwillMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
Goodwill. | RME | GMP | Maximum |  |
Annual revenue growth rate (as a percent) | 5.00%us-gaap_FairValueInputsLongTermRevenueGrowthRate / us-gaap_FairValueByAssetClassAxis = us-gaap_GoodwillMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_StatementBusinessSegmentsAxis = ttek_ResourceManagementAndEnergyMember / us-gaap_SubsegmentsAxis = ttek_GlobalMiningPracticeMember |
Income approach |  |
Weighted rate used in fair value of goodwill (as a percent) | 70.00%ttek_GoodwillFairValueWeightedPercentage / us-gaap_ValuationTechniqueAxis = us-gaap_IncomeApproachValuationTechniqueMember |
Discounted cash flow and market approach |  |
Weighted rate used in fair value of goodwill (as a percent) | 30.00%ttek_GoodwillFairValueWeightedPercentage / us-gaap_ValuationTechniqueAxis = us-gaap_MarketApproachValuationTechniqueMember |

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