Income Taxes (Components of Benefit from Income Taxes) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Domestic	$ (5,272)	$ 6,989	$ (5,719)	$ (90,143)
Foreign	4,314	(4,996)	5,747	13,167
(Benefit) provision for income taxes	$ (958)	$ 1,993	$ 28	$ (76,976)
Effective tax rate	4.40%	(1.20%)	(0.90%)	39.10%