Restructuring and Other Charges, net (Additional Information) (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring Charges and Other Expenses	$ 6,329	$ 9,858	$ 13,012	$ 24,499
Restructuring Reserve	17,694		$ 17,694		$ 7,209
Document Fiscal Year Focus			2020	2019
Restructuring charges	$ 2,820	$ 6,978	$ 6,868	$ 13,000
Restructuring and Related Cost, Expected Number of Positions Eliminated	38	178	75	274
Proceeds from Insurance Claims		$ 800	$ 100	$ 300
Asset Impairment for Regulatory Action [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2,000
Personnel
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	1,750		1,750		3,587
Restructuring charges	1,422	6,352	4,335	12,565
Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	15,944		15,944		$ 3,622
Restructuring charges	1,398	626	2,533	476
Other Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1,500	1,500	12,600	8,700
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring Charges and Other Expenses	5,075	3,728	7,511	10,663
Restructuring charges	1,566	1,409	1,367	2,272
Corporate | Personnel
Restructuring Cost and Reserve [Line Items]
Restructuring charges	683	797	1,016	1,950
Corporate | Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 883	612	351	322
Other Restructuring [Member] | Corporate, Non-Segment [Member] | Stand-up and separation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 4,200
Other Restructuring [Member] | Corporate, Non-Segment [Member] | Accelerated depreciation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 600		$ 3,100