Restructuring and Other Charges, net (Accrual Activity Relating to Restructuring and Other Charges) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Restructuring Cost and Reserve [Line Items]
Lease Obligation Incurred			$ 11,674
Restructuring [Roll Forward]
Balance at September 30, 2019			7,209
Restructuring charges	$ 564	$ 1,686	7,432	$ 14,727
Restructuring Reserve, Accrual Adjustment			1,263
Cash payments			(12,339)
Balance at June 30, 2020	15,239		15,239
Personnel
Restructuring Cost and Reserve [Line Items]
Lease Obligation Incurred			0
Restructuring [Roll Forward]
Balance at September 30, 2019			3,587
Restructuring charges	443	1,316	4,778	13,881
Restructuring Reserve, Accrual Adjustment			0
Cash payments			(7,214)
Balance at June 30, 2020	1,151		1,151
Facilities
Restructuring Cost and Reserve [Line Items]
Lease Obligation Incurred			11,674
Restructuring [Roll Forward]
Balance at September 30, 2019			3,622
Restructuring charges	121	$ 370	2,654	$ 846
Restructuring Reserve, Accrual Adjustment			1,263
Cash payments			(5,125)
Balance at June 30, 2020	$ 14,088		$ 14,088