Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Numerator
Net income	$ 93,559	$ 87,678
Denominator
Weighted average shares outstanding — basic (shares)	60,810	61,440
Dilutive effect of common shares from stock options and restricted stock units	1,072	842
Weighted average shares outstanding — diluted (shares)	61,882	62,282
Basic net income per share (dollars per share)	$ 1.54	$ 1.43
Diluted net income per share (dollars per share)	$ 1.51	$ 1.41