Summary of Significant Accounting Policies - Shares Used in Computing Basic and Diluted Earnings Per Share (Details) - shares		12 Months Ended
	Aug. 21, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Weighted-average common shares outstanding for basic computation (in shares)		209,063,000	208,928,000	178,417,000
Incremental shares issuable for stock options, common stock awards and Equity Units (in shares)		3,063,000	941,000	2,694,000
Weighted-average common shares outstanding for diluted computation (in shares)		212,126,000	209,869,000	181,111,000
Antidilutive securities excluded from computation of earnings per share (in shares)		5,267,000	7,056,000	1,162,000
Common Stock | Merger Sub
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Consideration paid (in shares)	34,612,847			34,613,000