Summary of Significant Accounting Policies - Shares Used in Computing Basic and Diluted Earnings Per Share (Details) - shares		1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 21, 2019	Aug. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Denominator:
Weighted-average common shares outstanding - basic (in shares)			208,598,000	174,759,000	208,989,000	174,541,000
Incremental shares issuable for stock options and awards (in shares)			377,000	0	1,020,000	2,848,000
Weighted-average common shares outstanding - diluted (in shares)			208,975,000	174,759,000	210,009,000	177,389,000
Business Acquisition [Line Items]
Antidilutive shares excluded from calculation of earnings per share (in USD per share)			7,083,000	2,576,000	7,083,000	244,000
Merger Sub | Common Stock
Business Acquisition [Line Items]
Shares issued in business acquisition (in shares)	34,612,847	34,613,000