Earnings per Share - Schedule of EPS, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net (loss) income	$ (680,808)	$ 167,365	$ 157,916
Weighted average shares outstanding, basic (in shares)	55,612,251	57,154,865	58,938,169
Dilutive effect of stock based compensation (in shares)	0	102,196	193,481
Weighted average shares outstanding, diluted (in shares)	55,612,251	57,257,061	59,131,650
Basic earnings per share (in dollars per share)	$ (12.24)	$ 2.93	$ 2.68
Diluted earnings per share (in dollars per share)	$ (12.24)	$ 2.92	$ 2.67
Performance stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share (in shares)	17,074	0
Stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share (in shares)	132,526	18,006