Derivative Liability, Fair Value, Gross Asset, Excluding Accrued Interest

No definition available.

Name:	ttek_DerivativeLiabilityFairValueGrossAssetExcludingAccruedInterest
Namespace Prefix:	ttek_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the number of derivative agreements entered into by the entity during the reporting period.

+ References

No definition available.

+ Details

Name:	ttek_DerivativeNumberOfAgreementsEnteredIntoByEntity
Namespace Prefix:	ttek_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual rate at which a foreign currency can be purchased or sold.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeForwardExchangeRate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value as of the balance sheet date of all foreign currency derivative assets not designated as hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959

+ Details

Name:	us-gaap_ForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate impact of foreign currency derivatives on earnings for the period. Includes impact of foreign currency cash flow hedge ineffectiveness and the ineffectiveness of fair value hedging derivatives and full change in fair value of the foreign currency derivatives not designated as hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (a)(2)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5624177-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5618551-113959

+ Details

Name:	us-gaap_GainLossOnForeignCurrencyDerivativesRecordedInEarningsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994

+ Details

Name:	us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after tax and reclassification, of gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI https://asc.fasb.org/extlink&oid=126968391&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=126968391&loc=SL7669646-108580

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ttek_RPSGroupPLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherNoncurrentAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ttek_InterestRateSwap1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ttek_InterestRateSwap2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ttek_InterestRateSwap3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ttek_InterestRateSwap4Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ttek_InterestRateSwap5Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivative Financial Instruments (Details) $ in Thousands, £ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Apr. 02, 2023 USD ($)	Jan. 01, 2023 USD ($)	Apr. 03, 2022 USD ($)	Apr. 02, 2023 USD ($)	Apr. 03, 2022 USD ($)	Sep. 30, 2018 agreement	Jan. 23, 2023 USD ($)	Dec. 28, 2022 USD ($)	Dec. 28, 2022 GBP (£)	Oct. 02, 2022 USD ($)	Oct. 02, 2022 GBP (£)
Derivative [Line Items]
Gains (losses) on cash flow hedges recognized in comprehensive income	$ (896)		$ 4,938	$ (985)	$ 7,604
RPS Group PLC
Derivative [Line Items]
Derivative, forward exchange rate								1.086	1.086	1.0852	1.0852
Foreign Exchange Forward \| RPS Group PLC
Derivative [Line Items]
Notional amount								$ 775,400	£ 714.0	$ 774,800	£ 714.0
Foreign currency forward contract, asset fair value							$ 109,300			19,900
Gain on foreign currency forward contract	21,400	$ 68,000
Interest Rate Swap \| Designated as cash flow hedges \| Derivatives designated as hedging instruments
Derivative [Line Items]
Notional amount	$ 193,800			$ 193,800
Number of derivative agreements \| agreement						5
Fixed rate	2.79%			2.79%
Credit to be reclassified during next twelve months	$ 1,400			$ 1,400
Interest Rate Swap \| Designated as cash flow hedges \| Derivatives designated as hedging instruments \| Other Noncurrent Assets
Derivative [Line Items]
Fair value gain of interest rate swap agreements	1,400			1,400						$ 2,400
Interest Rate Swap 1 \| Designated as cash flow hedges \| Derivatives designated as hedging instruments
Derivative [Line Items]
Notional amount	38,800			38,800
Interest Rate Swap 2 \| Designated as cash flow hedges \| Derivatives designated as hedging instruments
Derivative [Line Items]
Notional amount	38,800			38,800
Interest Rate Swap 3 \| Designated as cash flow hedges \| Derivatives designated as hedging instruments
Derivative [Line Items]
Notional amount	38,800			38,800
Interest Rate Swap 4 \| Designated as cash flow hedges \| Derivatives designated as hedging instruments
Derivative [Line Items]
Notional amount	38,800			38,800
Interest Rate Swap 5 \| Designated as cash flow hedges \| Derivatives designated as hedging instruments
Derivative [Line Items]
Notional amount	$ 38,800			$ 38,800