Basis of Presentation and Preparation (Details 2)	12 Months Ended
Sep. 27, 2015 item
Goodwill and Intangible Assets
Number of levels below reportable segments at which goodwill impairment testing is performed	1
Number of steps involved in process of goodwill annual impairment test	2

Represents the number of levels below reportable segments at which the reporting units reside for which goodwill impairment testing is performed.

No definition available.

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