Acquisitions - Allocation of Purchase Price of Assets Acquired and Liabilities Assumed (Detail)) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Jun. 30, 2018
Previously Reported/As Adjusted
Goodwill	$ 1,239,009		$ 319,778	$ 270,678
Finisar Corporation
Previously Reported/As Adjusted
Cash and cash equivalents	842,477	$ 842,764
Accounts receivable	259,341	260,864
Inventories	439,708	437,867
Property, plant & equipment	657,713	748,858
Intangible assets	665,200	827,689
Other assets	76,468	82,624
Deferred tax assets	16,267	0
Accounts payable	(123,707)	(123,707)
Other accrued liabilities	(202,116)	(148,425)
Deferred tax liabilities	(67,040)	(197,809)
Debt	(575,000)	(575,000)
Goodwill	919,192	759,239
Total Purchase Price	2,908,503	$ 2,914,964
Measurement Period Adjustments
Accounts receivable	(1,523)
Inventories	1,841
Property, plant, and equipment	(91,145)
Intangibles assets	(162,489)
Other assets	(6,443)
Deferred tax assets	16,267
Other accrued liabilities	(9,727)
Deferred tax liabilities	86,805
Goodwill	159,953
Total Purchase Price	(6,461)
Right-of-use asset decrease	16,000
Reduction to lease liability	16,000
Uncertain tax positions	(11,500)
Warranty reserve	(13,400)
Other current liabilities	5,500
Other liabilities, litigation and related insurance recovery	6,800
Finisar Corporation | Reclassification, Other
Previously Reported/As Adjusted
Cash and cash equivalents	(287)
Other assets	287
Other accrued liabilities	(43,964)
Deferred tax liabilities	$ 43,964