Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Mar. 29, 2015	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014
Consolidated Statements of Comprehensive Income
Net income including noncontrolling interests	$ 19,010us-gaap_ProfitLoss	$ 31,909us-gaap_ProfitLoss	$ 44,656us-gaap_ProfitLoss	$ 59,236us-gaap_ProfitLoss
Other comprehensive income, net of tax:
Foreign currency translation adjustments	(43,680)	(15,684)	(68,189)	(37,819)
(Loss) gain on cash flow hedge valuations, net of tax	(1,517)	(386)	(1,997)	439
Other comprehensive loss, net of tax	(45,197)	(16,070)	(70,186)	(37,380)
Comprehensive income (loss) including noncontrolling interests	(26,187)	15,839	(25,530)	21,856
Net loss (income) attributable to noncontrolling interests	7	(200)	(64)	(213)
Foreign currency translation adjustments	164	34	104	73
Comprehensive (income) loss attributable to noncontrolling interests	171	(166)	40	(140)
Comprehensive income (loss) attributable to Tetra Tech	$ (26,016)us-gaap_ComprehensiveIncomeNetOfTax	$ 15,673us-gaap_ComprehensiveIncomeNetOfTax	$ (25,490)us-gaap_ComprehensiveIncomeNetOfTax	$ 21,716us-gaap_ComprehensiveIncomeNetOfTax

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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