Goodwill and Intangible Assets - Amortization Expense Associated with Intangible Assets (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets	[1]	$ 1,684	$ 3,312	$ 3,472	$ 6,632
Cost of revenues
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets		615	1,687	1,321	3,373
Selling, general and administrative expenses
Finite-Lived Intangible Assets [Line Items]
Amortization expense of intangible assets		$ 1,069	$ 1,625	$ 2,151	$ 3,259

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