Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Sep. 30, 2012
Current assets:
Cash and cash equivalents	$ 146,335	$ 104,848
Accounts receivable - net	632,220	700,480
Prepaid expenses and other current assets	46,433	48,168
Income taxes receivable	25,635	5,817
Total current assets	850,623	859,313
Property and equipment - net	87,376	74,309
Investments in and advances to unconsolidated joint ventures	2,733	3,279
Goodwill	710,321	635,958
Intangible assets - net	94,754	74,231
Other long-term assets	25,705	23,940
Total assets	1,771,512	1,671,030
Current liabilities:
Accounts payable	133,092	154,003
Accrued compensation	118,737	128,086
Billings in excess of costs on uncompleted contracts	85,352	90,909
Deferred income taxes	9,642	20,809
Current portion of long-term debt	4,043	2,031
Estimated contingent earn-out liabilities	24,178	35,407
Other current liabilities	87,177	72,549
Total current liabilities	462,221	503,794
Deferred income taxes	26,738	24,268
Long-term debt	208,396	81,047
Long-term estimated contingent earn-out liabilities	68,140	16,132
Other long-term liabilities	29,061	25,922
Commitments and contingencies
Equity:
Preferred stock - Authorized, 2,000 shares of $0.01 par value; no shares issued and outstanding at June 30, 2013, and September 30, 2012
Common stock - Authorized, 150,000 shares of $0.01 par value; issued and outstanding, 64,799 and 63,837 shares at June 30, 2013, and September 30, 2012, respectively	648	638
Additional paid-in capital	457,480	433,009
Accumulated other comprehensive (loss) income	(9,021)	31,017
Retained earnings	526,964	554,306
Tetra Tech stockholders' equity	976,071	1,018,970
Noncontrolling interests	885	897
Total equity	976,956	1,019,867
Total liabilities and equity	$ 1,771,512	$ 1,671,030