Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 15,000	$ 17,442	$ 14,626	$ 30,549
Basic weighted average shares outstanding (in shares)	99,136,015	98,709,557	99,116,250	98,512,601
Dilutive effect of stock options and restricted stock awards/units (in shares)	383,910	308,429	325,135	387,836
Dilutive weighted average shares outstanding (in shares)	99,519,925	99,017,986	99,441,385	98,900,437
Basic net income per share (in dollars per share)	$ 0.15	$ 0.18	$ 0.15	$ 0.31
Diluted net income per share (in dollars per share)	$ 0.15	$ 0.18	$ 0.15	$ 0.31
Common stock equivalents not included in diluted calculation due to anti-dilutive effect (in shares)	2,337,503	2,754,963	3,115,284	2,181,968