Restructuring and Other Charges, net (Additional Information) (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring Charges and Other Expenses	$ 1,920	$ 1,947	$ 14,932	$ 26,446
Restructuring Reserve	15,239		$ 15,239		$ 7,209
Document Fiscal Year Focus			2020
Restructuring charges	$ 564	$ 1,686	$ 7,432	$ 14,727
Restructuring and Related Cost, Expected Number of Positions Eliminated	111	31	186	305
Proceeds from Insurance Claims	$ 900	$ 400		$ 700
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	1,151		1,151		3,587
Restructuring charges	443	1,316	4,778	13,881
Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	14,088		14,088		$ 3,622
Restructuring charges	121	370	2,654	846
Other Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	400	400		9,200
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring Charges and Other Expenses	1,810	1,106	9,321	11,769
Restructuring charges	454	1,084	1,821	3,356
Corporate | Personnel
Restructuring Cost and Reserve [Line Items]
Restructuring charges	445	730	1,461	2,680
Corporate | Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 9	354	360	676
Other Restructuring [Member] | Corporate, Non-Segment [Member] | Stand-up and separation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 4,600
Other Restructuring [Member] | Corporate, Non-Segment [Member] | Accelerated depreciation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 200		$ 3,300