Earnings per Share - Schedule of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 5,400	$ 26,783	$ (691,944)	$ 117,080
Weighted average common shares outstanding (in shares)	55,082,621	56,995,007	55,788,751	57,321,561
Dilutive effect of stock based compensation (in shares)	62,998	115,096	0	86,462
Weighted average common shares outstanding for diluted earnings per share calculation (in shares)	55,145,619	57,110,103	55,788,751	57,408,023
Basic earnings per share (in dollars per share)	$ 0.10	$ 0.47	$ (12.40)	$ 2.04
Diluted earnings per share (in dollars per share)	$ 0.10	$ 0.47	$ (12.40)	$ 2.04