Condensed Consolidated Balance Sheets (USD $) In Thousands	9 Months Ended	12 Months Ended
	Jul. 03, 2011	Oct. 03, 2010
CURRENT ASSETS:
Cash and cash equivalents	$ 98,366	$ 220,933
Accounts receivable - net	669,131	566,642
Prepaid expenses and other current assets	53,022	49,889
Income taxes receivable	9,392	7,249
Total current assets	829,911	844,713
PROPERTY AND EQUIPMENT:
Land and buildings	11,729	11,707
Equipment, furniture and fixtures	159,327	145,210
Leasehold improvements	23,888	18,104
Total	194,944	175,021
Accumulated depreciation and amortization	(114,393)	(95,638)
PROPERTY AND EQUIPMENT - NET	80,551	79,383
INVESTMENTS IN AND ADVANCES TO UNCONSOLIDATED JOINT VENTURES	3,427	140
GOODWILL	564,126	394,422
INTANGIBLE ASSETS - NET	71,703	45,995
OTHER ASSETS	22,109	17,036
TOTAL ASSETS	1,571,827	1,381,689
CURRENT LIABILITIES:
Accounts payable	184,391	166,450
Accrued compensation	120,467	93,243
Billings in excess of costs on uncompleted contracts	83,907	79,401
Deferred income taxes	18,145	21,851
Current portion of long-term debt	2,830	5,002
Contingent earn-out liabilities	27,512	10,513
Other current liabilities	74,112	90,747
Total current liabilities	511,364	467,207
DEFERRED INCOME TAXES	27,663	12,506
LONG-TERM DEBT	112,744	122,510
OTHER LONG-TERM LIABILITIES	51,951	31,333
COMMITMENTS AND CONTINGENCIES
STOCKHOLDERS' EQUITY:
Preferred stock - Authorized, 2,000 shares of $0.01 par value; no shares issued and outstanding as of July 3, 2011 and October 3, 2010
Common stock - Authorized, 150,000 shares of $0.01 par value; issued and outstanding, 62,464 and 61,755 shares as of July 3, 2011 and October 3, 2010, respectively	625	618
Additional paid-in capital	389,634	368,865
Accumulated other comprehensive income	40,159	18,763
Retained earnings	423,526	359,887
Total Tetra Tech stockholders' equity	853,944	748,133
Noncontrolling interests	14,161
TOTAL STOCKHOLDERS' EQUITY	868,105	748,133
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 1,571,827	$ 1,381,689