Goodwill and Intangible Assets - Amortization Expense Associated with Intangible Assets (Detail) - USD ($) $ in Thousands		3 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets	[1]	$ 1,788	$ 3,320
Cost of revenues
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets		706	1,686
Selling, general and administrative expenses
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets		$ 1,082	$ 1,634

[1] Cost of revenues and selling, general and administrative expenses exclude the amortization of intangible assets. See Note 4.