Income Taxes - Reconciliation Between Federal Statutory Income Tax Rate and Effective Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Income Tax Disclosure [Abstract]
Income tax provision at U.S. federal statutory rate	$ 38,233	$ 46,595	$ 46,194
State income taxes, net of U.S. federal benefit	1,719	2,832	2,689
Foreign tax rate differential	(5,279)	(4,592)	(2,855)
Intercompany interest	(1,260)	(1,246)	0
Research credits	(2,104)	(302)	(2,412)
Domestic production deduction	(1,607)	(3,141)	(2,168)
Federal and state audit settlements	(5,806)	(5,886)	0
Foreign	(3,109)	(1,654)	0
Valuation allowance	1,805	3,888	2,310
Intercompany dividend	(1,296)	150	(32)
Other	1,440	1,608	(1,837)
Total provision	$ 22,736	$ 38,252	$ 41,889