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, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Weighted-average common shares outstanding for basic computation (in shares)			189,905,000	174,759,000	174,501,000	174,413,000	174,391,000	173,991,000	173,570,000	173,670,000	178,417,000	173,908,000	173,662,000
Incremental shares issuable for stock options and common stock awards (in shares)											2,694,000	2,997,000	3,497,000
Weighted-average common shares outstanding for diluted computation (in shares)			189,905,000	174,759,000	177,318,000	177,566,000	177,506,000	176,807,000	176,350,000	176,948,000	181,111,000	176,905,000	177,159,000
Antidilutive securities excluded from computation of earnings per share (in shares)											1,162,000		146,000
Common Stock | Merger Sub
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Consideration paid (in shares)	34,612,847	34,612,847									34,613,000