Restructuring and Other Charges, net (Additional Information) (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)
Restructuring Cost and Reserve [Line Items]
Document Period End Date			Mar. 31, 2019
Restructuring Charges and Other Expenses	$ 21,469	$ 8,881	$ 44,550	$ 22,450
Restructuring Reserve	14,591		$ 14,591		$ 16,193
Document Fiscal Year Focus			2019
Restructuring charges	10,190	5,067	$ 20,579	$ 10,383
Number of personnel eliminated			360	160
Professional service fees			$ 456	$ 1,451
Tangible Asset Impairment Charges	(800)	1,500	(300)	7,200
Personnel
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	10,076		10,076		9,690
Restructuring charges	9,945	3,704	18,428	7,364
Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	4,515		4,515		$ 6,503
Restructuring charges	245	1,363	2,151	3,019
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Other Charges	11,279	3,814	23,971	12,067
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring Charges and Other Expenses	3,728	5,319	10,663	13,317
Restructuring charges	1,409	1,505	2,272	1,250
Corporate | Personnel
Restructuring Cost and Reserve [Line Items]
Restructuring charges	797	707	1,950	1,192
Corporate | Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring charges	612	798	322	58
Corporate | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Other Charges	2,319	3,814	8,391	12,067
Corporate | Chief Executive Officer [Member] | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Other Charges		$ 2,300		$ 5,700
Corporate transformation [Member] | Corporate | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Other Charges	1,500		8,700
Stand-up and separation [Member] | Corporate | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Other Charges	8,300		12,500
Accelerated depreciation [Member] | Corporate | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Other Charges	$ 600		$ 3,100