Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Paragraph 1
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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Amount of cash inflow from realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

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Amount of cash outflow for realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Nature of Business and Summary of Significant Accounting Policies - New Accounting Pronouncements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax benefit related to share-based compensation expense	$ 20,400	$ 18,700	$ 16,100
Debt issuance costs, net	199	376
Accounting Standards Update 2015-03 [Member] \| Other noncurrent assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs, net		400
Accounting Standards Update 2015-03 [Member] \| Long-term debt
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs, net		400
New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax benefit related to share-based compensation expense	$ 24,700
New Accounting Pronouncement, Early Adoption, Effect [Member] \| Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase to operating activities		25,000	(13,800)
Increase to financing activities		$ 25,000	$ 13,800