Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 27, 2016	Mar. 29, 2015	Mar. 27, 2016	Mar. 29, 2015
Condensed Consolidated Statements of Income
Revenue	$ 627,384	$ 564,763	$ 1,188,092	$ 1,145,819
Subcontractor costs	(148,619)	(132,009)	(288,371)	(275,985)
Other costs of revenue	(403,976)	(362,957)	(751,772)	(721,238)
Gross profit	74,789	69,797	147,949	148,596
Selling, general and administrative expenses	(40,406)	(42,512)	(79,634)	(84,699)
Acquisition and integration expenses	(15,911)		(15,911)
Contingent consideration - fair value adjustments	(1,822)	3,113	(2,823)	3,113
Operating income	16,650	30,398	49,581	67,010
Interest expense	(4,251)	(1,804)	(5,911)	(3,594)
Income before income tax expense	12,399	28,594	43,670	63,416
Income tax expense	(8,661)	(9,584)	(16,692)	(18,760)
Net income including noncontrolling interests	3,738	19,010	26,978	44,656
Net (income) loss from noncontrolling interests	6	7	5	(64)
Net income attributable to Tetra Tech	$ 3,744	$ 19,017	$ 26,983	$ 44,592
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.06	$ 0.31	$ 0.46	$ 0.72
Diluted (in dollars per share)	$ 0.06	$ 0.31	$ 0.45	$ 0.71
Weighted-average common shares outstanding:
Basic (in shares)	58,451	61,153	58,819	61,816
Diluted (in shares)	59,131	61,723	59,527	62,431
Cash dividends paid per share	$ 0.08	$ 0.07	$ 0.16	$ 0.14