Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 49,251	$ 33,345	$ 147,227	$ 108,144
Other comprehensive income, net of tax
Foreign currency translation adjustments	5,428	(13,209)	(8,661)	(32,792)
Loss on cash flow hedge valuations	(4,289)	(485)	(11,067)	(446)
Other comprehensive income (loss) attributable to Tetra Tech	1,139	(13,694)	(19,728)	(33,238)
Other comprehensive income (loss) attributable to noncontrolling interests	3	(2)	242	(10)
Comprehensive income attributable to Tetra Tech	50,372	19,628	127,413	74,844
Comprehensive income attributable to noncontrolling interests	21	21	328	52
Comprehensive income	$ 50,393	$ 19,649	$ 127,741	$ 74,896

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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