Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Apr. 01, 2018	Apr. 02, 2017	Apr. 01, 2018	Apr. 02, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 28,747	$ 26,867	$ 74,799	$ 53,456
Foreign currency translation adjustments	(16,121)	9,328	(19,590)	(6,671)
Gain (loss) on cash flow hedge valuations	(27)	452	39	1,448
Other comprehensive income (loss), net of tax	(16,148)	9,780	(19,551)	(5,223)
Comprehensive income, net of tax	12,599	36,647	55,248	48,233
Net income attributable to noncontrolling interests	(22)	(5)	(40)	(32)
Foreign currency translation adjustments	5	(5)	7	(188)
Comprehensive income attributable to noncontrolling interests	(17)	(10)	(33)	(220)
Comprehensive income attributable to Tetra Tech, net of tax	$ 12,582	$ 36,637	$ 55,215	$ 48,013

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

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Amount of Net Income (Loss) attributable to noncontrolling interest.

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to noncontrolling interests.

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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