Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2019	Apr. 01, 2018
Revenue	$ 722,621	$ 700,262	$ 1,440,052	$ 1,460,010
Gross profit	96,471	91,425	195,155	185,570
Selling, general and administrative expenses	(48,898)	(46,791)	(91,871)	(92,347)
Contingent consideration – fair value adjustments	(28)	(1,918)	(28)	(1,918)
Income from operations	47,545	42,716	103,256	91,305
Interest expense	(3,164)	(4,092)	(6,061)	(7,252)
Income before income tax benefit (expense)	44,381	38,624	97,195	84,053
Income tax benefit (expense)	11,563	(9,877)	781	(9,254)
Net income	55,944	28,747	97,976	74,799
Net income attributable to noncontrolling interests	(33)	(22)	(69)	(40)
Net income attributable to Tetra Tech	$ 55,911	$ 28,725	$ 97,907	$ 74,759
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 1.01	$ 0.51	$ 1.77	$ 1.34
Diluted (in dollars per share)	$ 1.00	$ 0.51	$ 1.74	$ 1.32
Weighted-average common shares outstanding:
Basic (in shares)	55,143	55,841	55,237	55,900
Diluted (in shares)	55,985	56,673	56,161	56,825
Subcontractor
Cost of revenue	$ (137,237)	$ (167,469)	$ (301,305)	$ (382,370)
Other
Cost of revenue	$ (488,913)	$ (441,368)	$ (943,592)	$ (892,070)