Income Taxes - Aggregate Changes in Balance of Company's Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Unrecognized tax benefits, Beginning balance	$ 196,668	$ 126,706	$ 123,942
Additions based on tax positions related to the current year	22,319	65,009	22,314
Additions for tax positions of prior years	12,261	41,183	11,125
Settlements with tax authorities	(9,450)	(31,624)	(13,443)
Lapse of statute of limitations	(28,774)	(4,606)	(17,232)
Unrecognized tax benefits, Ending balance	$ 193,024	$ 196,668	$ 126,706

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- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=SL6600010-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Unrecognized Tax Benefit
-URI http://asc.fasb.org/extlink&oid=6527854

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

+ References

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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