Comprehensive Income (Details) (USD $) In Thousands	12 Months Ended
Oct. 02, 2011	Oct. 03, 2010	Sep. 27, 2009
Comprehensive Income.
Net income including noncontrolling interests	$ 92,982	$ 76,819	$ 87,028
Other comprehensive income:
Foreign currency translation adjustment	(13,955)	6,874	12,211
Foreign currency hedge	438	(337)
Comprehensive income	79,465	83,356	99,239
Net income attributable to noncontrolling interests	(2,943)
Foreign currency translation adjustment	(492)
Comprehensive income attributable to noncontrolling interests	(3,435)
Comprehensive income attributable to Tetra Tech	$ 76,030	$ 83,356	$ 99,239

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