Summary of Significant Accounting Policies - Shares Used in Computing Basic and Diluted Earnings Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Denominator:
Weighted-average common shares outstanding - basic (in shares)	174,759,000	173,991,000	174,541,000	173,744,000
Incremental shares issuable for stock options and awards (in shares)	0	2,816,000	2,848,000	2,958,000
Weighted-average common shares outstanding - diluted (in shares)	174,759,000	176,807,000	177,389,000	176,702,000
Antidilutive shares excluded from calculation of earnings per share (in USD per share)	2,576,000	0	244,000	0