Debt - Components of Debt (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 24, 2019
Line of Credit Facility [Line Items]
Total debt	$ 1,530,146	$ 2,255,342
Current portion of long-term debt	(62,050)	(69,250)
Long-term debt, less current portion	$ 1,468,096	2,186,092
0.50% Convertible Senior Notes
Line of Credit Facility [Line Items]
Debt instrument, interest rate	0.50%			0.50%
Total debt, gross	$ 14,900
0.50% Convertible Senior Notes | Finisar Corporation
Line of Credit Facility [Line Items]
Total debt, gross	$ 14,888	14,888
0.25% Convertible Senior Note Due 2022
Line of Credit Facility [Line Items]
Debt instrument, interest rate	0.25%		0.25%
Total debt, gross	$ 345,000	345,000
0.25% convertible senior notes unamortized discount attributable to cash conversion option and debt issuance costs including initial purchaser discount	(27,281)	(30,688)
Term A Loan Facility
Line of Credit Facility [Line Items]
Total debt, gross	$ 1,178,950	1,194,463
Term A Loan Facility | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, rate added on variable rate	2.00%
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total debt, gross	$ 49,000	74,000
Revolving Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, rate added on variable rate	2.00%
Term A Facility and Revolving Credit Facility
Line of Credit Facility [Line Items]
Credit facility unamortized debt issuance costs	$ (30,411)	(32,174)
Term B Loan Facility
Line of Credit Facility [Line Items]
Total debt, gross	0	714,600
Credit facility unamortized debt issuance costs	$ 0	$ (24,747)
Term B Loan Facility | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, rate added on variable rate		3.50%