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, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Denominator (thousands of shares):
Weighted-average common shares outstanding - basic (in shares)		173,624	172,619	173,567	172,733
Incremental shares issuable for stock options and awards (in shares)	[1]	3,512	2,226	3,409	2,220
Weighted-average common shares outstanding - diluted (in shares)		177,136	174,845	176,976	174,953

[1] See “Adoption of New Accounting Standard — Employee Share-based Payments” below for the impact on the calculation of diluted shares for the three and six months ended March 31, 2017 resulting from the adoption of new accounting guidance regarding share-based payments.