Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2013	Jul. 01, 2012	Jun. 30, 2013	Jul. 01, 2012
Condensed Consolidated Statements of Operations
Revenue	$ 614,835	$ 684,698	$ 1,915,379	$ 1,991,670
Subcontractor costs	(139,693)	(167,832)	(422,092)	(505,855)
Other costs of revenue	(469,398)	(419,140)	(1,314,219)	(1,215,391)
Selling, general and administrative expenses	(56,744)	(53,210)	(151,539)	(154,487)
Contingent consideration - fair value adjustments	7,716	1,745	8,662	1,959
Impairment of goodwill	(56,600)		(56,600)
Operating (loss) income	(99,884)	46,261	(20,409)	117,896
Interest expense - net	(2,010)	(1,419)	(5,330)	(4,182)
(Loss) income before income tax expense	(101,894)	44,842	(25,739)	113,714
Income tax benefit (expense)	23,779	(15,674)	(1,108)	(39,522)
Net (loss) income including noncontrolling interests	(78,115)	29,168	(26,847)	74,192
Net income attributable to noncontrolling interests	(270)	(114)	(495)	(244)
Net (loss) income attributable to Tetra Tech	$ (78,385)	$ 29,054	$ (27,342)	$ 73,948
Net (loss) income attributable to Tetra Tech per share:
Basic (in dollars per share)	$ (1.21)	$ 0.46	$ (0.42)	$ 1.17
Diluted (in dollars per share)	$ (1.21)	$ 0.45	$ (0.42)	$ 1.16
Weighted-average common shares outstanding:
Basic (in shares)	64,832	63,387	64,554	63,054
Diluted (in shares)	64,832	64,179	64,554	63,752