Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 29, 2014	Jun. 30, 2013	Jun. 29, 2014	Jun. 30, 2013
Condensed Consolidated Statements of Operations
Revenue	$ 629,502	$ 614,835	$ 1,861,635	$ 1,915,379
Subcontractor costs	(170,746)	(139,693)	(463,904)	(422,092)
Other costs of revenue	(381,319)	(469,398)	(1,164,761)	(1,314,219)
Selling, general and administrative expense	(47,175)	(56,744)	(138,778)	(151,539)
Contingent consideration - fair value adjustments	8,905	7,716	34,878	8,662
Impairment of goodwill		(56,600)		(56,600)
Operating income (loss)	39,167	(99,884)	129,070	(20,409)
Interest expense	(2,454)	(2,010)	(7,373)	(5,330)
Income (loss) before income tax (expense) benefit	36,713	(101,894)	121,697	(25,739)
Income tax (expense) benefit	(10,002)	23,779	(35,751)	(1,108)
Net income (loss) including noncontrolling interests	26,711	(78,115)	85,946	(26,847)
Net income attributable to noncontrolling interests	(54)	(270)	(266)	(495)
Net income (loss) attributable to Tetra Tech	$ 26,657	$ (78,385)	$ 85,680	$ (27,342)
Net income (loss) per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.41	$ (1.21)	$ 1.32	$ (0.42)
Diluted (in dollars per share)	$ 0.41	$ (1.21)	$ 1.31	$ (0.42)
Weighted-average common shares outstanding:
Basic (in shares)	64,566	64,832	64,683	64,554
Diluted (in shares)	65,302	64,832	65,493	64,554
Cash dividends paid per share	$ 0.07		$ 0.07