Condensed Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jul. 01, 2012	Jul. 03, 2011	Jul. 01, 2012	Jul. 03, 2011
Revenue	$ 684,698	$ 673,792	$ 1,991,670	$ 1,897,482
Subcontractor costs	(167,832)	(193,288)	(505,855)	(581,093)
Other costs of revenue	(419,140)	(395,630)	(1,215,391)	(1,076,788)
Selling, general and administrative expenses	(51,465)	(45,466)	(152,528)	(136,612)
Operating income	46,261	39,408	117,896	102,989
Interest expense - net	(1,419)	(1,703)	(4,182)	(4,478)
Income before income tax expense	44,842	37,705	113,714	98,511
Income tax expense	(15,674)	(12,957)	(39,522)	(32,928)
Net income including noncontrolling interests	29,168	24,748	74,192	65,583
Net income attributable to noncontrolling interests	(114)	(909)	(244)	(1,944)
Net income attributable to Tetra Tech	$ 29,054	$ 23,839	$ 73,948	$ 63,639
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.46	$ 0.38	$ 1.17	$ 1.03
Diluted (in dollars per share)	$ 0.45	$ 0.38	$ 1.16	$ 1.01
Weighted-average common shares outstanding:
Basic (in shares)	63,387	62,203	63,054	61,967
Diluted (in shares)	64,179	62,934	63,752	62,745