Condensed Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 30, 2014	Mar. 31, 2013	Mar. 30, 2014	Mar. 31, 2013
Condensed Consolidated Statements of Income
Revenue	$ 586,285	$ 641,999	$ 1,232,133	$ 1,300,544
Subcontractor costs	(130,300)	(121,052)	(293,158)	(282,399)
Other costs of revenue	(386,913)	(435,827)	(783,442)	(844,822)
Selling, general and administrative expenses	(44,229)	(48,409)	(91,602)	(94,793)
Contingent consideration - fair value adjustments	21,343	956	25,973	946
Operating income	46,186	37,667	89,904	79,476
Interest expense	(2,496)	(2,136)	(4,919)	(3,320)
Income before income tax expense	43,690	35,531	84,985	76,156
Income tax expense	(11,781)	(10,659)	(25,749)	(24,888)
Net income including noncontrolling interests	31,909	24,872	59,236	51,268
Net income attributable to noncontrolling interests	(200)	(52)	(213)	(225)
Net income attributable to Tetra Tech	$ 31,709	$ 24,820	$ 59,023	$ 51,043
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.49	$ 0.38	$ 0.91	$ 0.79
Diluted (in dollars per share)	$ 0.48	$ 0.38	$ 0.90	$ 0.78
Weighted-average common shares outstanding:
Basic (in shares)	64,835	64,551	64,670	64,376
Diluted (in shares)	65,710	65,472	65,517	65,208