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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Denominator:
Weighted-average common shares outstanding - basic (in shares)	173,991,000	173,742,000	173,744,000	173,625,000
Incremental shares issuable for stock options and awards (in shares)	2,816,000	0	2,958,000	3,500,000
Weighted-average common shares outstanding - diluted (in shares)	176,807,000	173,742,000	176,702,000	177,125,000
Antidilutive shares excluded from calculation of earnings per share	0	3,556,000	0	0