Earnings Per Share ("EPS") (Tables)

3 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

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

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

	Three Months Ended
	December 31, 2017		January 1, 2017
	(in thousands, except per share data)
Net income attributable to Tetra Tech	$	46,034	$	26,562
Weighted-average common shares outstanding – basic	55,855		57,099
Effect of dilutive stock options and unvested restricted stock	1,020		1,046
Weighted-average common stock outstanding – diluted	56,875		58,145
Earnings per share attributable to Tetra Tech:
Basic	$	0.82	$	0.47
Diluted	$	0.81	$	0.46