Summary of Significant Accounting Policies - Shares Used in Computing Basic and Diluted Earnings Per Share (Details) - shares			3 Months Ended								12 Months Ended
	Aug. 21, 2019	Aug. 01, 2019	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Weighted-average common shares outstanding for basic computation (in shares)			208,655,000	208,598,000	208,941,000	209,439,000	189,905,000	174,759,000	174,501,000	174,413,000	208,928,000	178,417,000	173,908,000
Incremental shares issuable for stock options and common stock awards (in shares)											941,000	2,694,000	2,997,000
Weighted-average common shares outstanding for diluted computation (in shares)			209,357,000	208,975,000	209,808,000	211,258,000	189,905,000	174,759,000	177,318,000	177,566,000	209,869,000	181,111,000	176,905,000
Antidilutive securities excluded from computation of earnings per share (in shares)											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										34,613,000