Represents the amount of remaining estimated costs to complete the contract.

No definition available.

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Namespace Prefix:	ttek_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_ChangeInAccountingEstimateLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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

- Definition

Cumulative provision for contract losses not offset against related costs accumulated on the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 605

-SubTopic 35

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57777-111642

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

Basis of Presentation and Preparation (Details 4) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 27, 2015	Jun. 28, 2015	Mar. 29, 2015	Dec. 28, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 29, 2013	Sep. 27, 2015	Sep. 28, 2014	Sep. 29, 2013
Revenue recognition and contract costs
Unfavorable operating income adjustments	$ 20,047	$ (40,721)	$ (30,398)	$ (36,612)	$ (24,762)	$ (39,167)	$ (46,186)	$ (43,718)	$ (87,684)	$ (153,833)	$ (20,218)
Liability for anticipated losses	10,500				$ 18,600				10,500	18,600
Estimated cost to complete the related contracts	$ 54,700								54,700
Contracts accounted for under the percentage-of-completion method of accounting
Revenue recognition and contract costs
Unfavorable operating income adjustments									$ 8,900	$ 35,900	$ 40,100