Condensed Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Dec. 30, 2012	Jan. 01, 2012
Condensed Consolidated Statements of Income
Revenue	$ 658,545	$ 682,627
Subcontractor costs	(161,347)	(190,571)
Other costs of revenue	(408,995)	(407,336)
Selling, general and administrative expenses	(46,394)	(48,627)
Operating income	41,809	36,093
Interest expense - net	(1,185)	(1,311)
Income before income tax expense	40,624	34,782
Income tax expense	(14,228)	(12,079)
Net income including noncontrolling interests	26,396	22,703
Net income attributable to noncontrolling interests	(172)	(93)
Net income attributable to Tetra Tech	$ 26,224	$ 22,610
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.41	$ 0.36
Diluted (in dollars per share)	$ 0.41	$ 0.36
Weighted-average common shares outstanding:
Basic (in shares)	63,864	62,433
Diluted (in shares)	64,608	63,068