Stockholders' Equity and Weighted Average Common Shares Outstanding - Components of Diluted Weighted Average Shares Outstanding (Details) - shares shares in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Equity [Abstract]
Weighted average common shares outstanding — basic (shares)	204,783	210,165	217,872
Effect of dilutive securities — stock options and restricted stock units (shares)	0	1,675	2,464
Weighted average common shares outstanding — diluted (shares)	204,783	211,840	220,336