Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Current:
Federal	$ 8,071	$ 19,576	$ 50,631
State	2,236	1,055	2,900
Foreign	9,559	8,486	7,597
Current income tax	19,866	29,117	61,128
Deferred:
Federal	28,013	(5,027)	(23,592)
State	132	(296)	(225)
Foreign	(2,416)	(726)	(2,190)
Deferred income taxes	25,729	(6,049)	(26,007)
Total provision	$ 45,595	$ 23,068	$ 35,121