Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jul. 01, 2018	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 33,345	$ 29,975	$ 108,144	$ 83,431
Other comprehensive income (loss), net of tax
Foreign currency translation adjustments	(13,209)	14,049	(32,792)	7,190
Gain (loss) on cash flow hedge valuations	(485)	138	(446)	1,586
Other comprehensive income (loss) attributable to Tetra Tech	(13,694)	14,187	(33,238)	8,776
Other comprehensive income (loss) attributable to noncontrolling interests	(2)	1	(10)	189
Comprehensive income	19,649	44,163	74,896	92,396
Comprehensive income attributable to Tetra Tech	19,628	44,170	74,844	92,183
Comprehensive income (loss) attributable to noncontrolling interests	$ 21	$ (7)	$ 52	$ 213

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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