Nature of Business New Accounting Pronouncements (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs, net	$ 328		$ 376
Accounting Standards Update 2015-03 | Other Noncurrent Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs, net			(400)
Accounting Standards Update 2015-03 | Long-term Debt
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt issuance costs, net			$ 400
New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Employee service share-based compensation, tax benefit from compensation expense	$ 17,300
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standard Updates 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefit from share-based compensation, operating activities		$ 10,100
Excess tax benefits from share-based compensation, financing activities		$ 10,100