Restructuring Charges - Charges Taken Related to Restructuring Actions (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 27, 2021	Sep. 25, 2021	Sep. 26, 2020	Sep. 28, 2019
Restructuring Cost and Reserve [Line Items]
Divestiture charges	$ 1,900,000
Fiscal 2019 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions				$ 5,400,000
Facility closure costs				1,200,000
Fiscal restructuring charges				6,600,000
Fiscal 2020 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions			$ 13,400,000
Facility closure costs			1,900,000
Fiscal restructuring charges		$ 8,700,000	15,300,000
Fiscal 2021 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions		9,300,000
Fiscal restructuring charges		9,300,000
Fiscal 2021 Actions | Fiscal 2019 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions				0
Facility closure costs				0
Fiscal restructuring charges				0
Fiscal 2021 Actions | Fiscal 2020 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions			0
Facility closure costs			0
Fiscal restructuring charges			0
Fiscal 2021 Actions | Fiscal 2021 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions		8,700,000
Fiscal restructuring charges		8,700,000
Fiscal 2020 Actions | Fiscal 2019 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions				0
Facility closure costs				0
Fiscal restructuring charges				0
Fiscal 2020 Actions | Fiscal 2020 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions			13,200,000
Facility closure costs			1,900,000
Fiscal restructuring charges			15,100,000
Fiscal 2020 Actions | Fiscal 2021 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions		600,000
Fiscal restructuring charges		600,000
Fiscal 2019 Actions | Fiscal 2019 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions				4,000,000.0
Facility closure costs				0
Fiscal restructuring charges				4,000,000.0
Fiscal 2019 Actions | Fiscal 2020 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions			300,000
Facility closure costs			0
Fiscal restructuring charges			300,000
Fiscal 2019 Actions | Fiscal 2021 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions		0
Fiscal restructuring charges		0
Other | Fiscal 2019 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions				1,400,000
Facility closure costs				1,200,000
Fiscal restructuring charges				$ 2,600,000
Other | Fiscal 2020 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions			(100,000)
Facility closure costs			0
Fiscal restructuring charges			$ (100,000)
Other | Fiscal 2021 restructuring charges | Restructuring Charges
Restructuring Cost and Reserve [Line Items]
Workforce reductions		0
Fiscal restructuring charges		$ 0