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Restructuring and Other Charges, net (Accrual Activity Relating to Restructuring and Other Charges) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Restructuring [Roll Forward]
Balance at September 30, 2018			$ 16,193
Restructuring charges	$ 10,190	$ 5,067	20,579	$ 10,383
Restructuring Reserve, Accrual Adjustment			504
Cash payments			(22,685)
Balance at March 31, 2019	14,591		14,591
Personnel
Restructuring [Roll Forward]
Balance at September 30, 2018			9,690
Restructuring charges	9,945	3,704	18,428	7,364
Restructuring Reserve, Accrual Adjustment			0
Cash payments			(18,042)
Balance at March 31, 2019	10,076		10,076
Facilities
Restructuring [Roll Forward]
Balance at September 30, 2018			6,503
Restructuring charges	245	$ 1,363	2,151	$ 3,019
Restructuring Reserve, Accrual Adjustment			504
Cash payments			(4,643)
Balance at March 31, 2019	$ 4,515		$ 4,515