Earnings per Share ("EPS") (Tables)

6 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

Schedule of number of weighted-average shares used to compute basic and diluted EPS

The following table presents the number of weighted-average shares used to compute basic and diluted EPS:

	Three Months Ended				Six Months Ended
	March 31, 2019		April 1, 2018		March 31, 2019		April 1, 2018
	(in thousands, except per share data)
Net income attributable to Tetra Tech	$	55,911	$	28,725	$	97,907	$	74,759
Weighted-average common shares outstanding – basic	55,143		55,841		55,237		55,900
Effect of dilutive stock options and unvested restricted stock	842		832		924		925
Weighted-average common shares outstanding – diluted	55,985		56,673		56,161		56,825
Earnings per share attributable to Tetra Tech:
Basic	$	1.01	$	0.51	$	1.77	$	1.34
Diluted	$	1.00	$	0.51	$	1.74	$	1.32