Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 27, 2015	Sep. 28, 2014	Sep. 29, 2013
Consolidated Statements of Operations
Revenue	$ 2,299,321	$ 2,483,814	$ 2,613,755
Subcontractor costs	(580,606)	(623,896)	(588,923)
Other costs of revenue	(1,402,925)	(1,577,481)	(1,757,842)
Selling, general and administrative expenses	(170,456)	(187,298)	(199,732)
Contingent consideration - fair value adjustments	3,113	58,694	9,560
Impairment of goodwill and other intangible assets	(60,763)		(56,600)
Operating income	87,684	153,833	20,218
Interest income	680	804	1,003
Interest expense	(8,043)	(10,294)	(8,689)
Income before income tax expense	80,321	144,343	12,532
Income tax expense	(41,093)	(35,668)	(14,038)
Net income (loss) including noncontrolling interests	39,228	108,675	(1,506)
Net income attributable to noncontrolling interests	(154)	(409)	(635)
Net income (loss) attributable to Tetra Tech	$ 39,074	$ 108,266	$ (2,141)
Net income (loss) attributable to Tetra Tech per share:
Basic (in dollars per share)	$ 0.64	$ 1.68	$ (0.03)
Diluted (in dollars per share)	$ 0.64	$ 1.66	$ (0.03)
Weighted-average common shares outstanding:
Basic (in shares)	60,913	64,379	64,544
Diluted (in shares)	61,532	65,146	64,544
Cash dividends paid per share	$ 0.30	$ 0.14