Summary of Significant Accounting Policies - Shares Used in Computing Basic and Diluted Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Denominator:
Weighted-average common shares outstanding - basic (in shares)	208,930	208,941	208,849	209,151
Incremental shares issuable for stock options and awards (in shares)	1,162	867	1,014	1,343
Weighted-average common shares outstanding - diluted (in shares)	210,092	209,808	209,863	210,494
Antidilutive securities excluded from computation of earnings per share (in shares)	5,102	8,020	5,102	8,020