Earnings Per Share - Additional Information (Detail)	3 Months Ended	6 Months Ended
Mar. 31, 2016 $ / shares	Mar. 31, 2015 $ / shares	Mar. 31, 2016 Quarter $ / shares	Mar. 31, 2015 Quarter $ / shares
Earnings Per Share [Abstract]
Number of potential dilutive shares due to stock options, unvested restricted stock and unvested performance share awards	3.9		4.5
Dividend declared \| $ / shares	$ 0.29	$ 0.26	$ 0.58	$ 0.52
Number of quarterly dividends declared \| Quarter			2	2

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would have been antidilutive for the period presented.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration