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RELATED-PARTY TRANSACTIONS - Equity Method Investment (Details)	1 Months Ended	3 Months Ended		6 Months Ended			12 Months Ended
	Oct. 31, 2013	Mar. 29, 2019 USD ($) member	Mar. 30, 2018 USD ($)	Sep. 27, 2019 USD ($)	Mar. 29, 2019 USD ($) member	Mar. 30, 2018 USD ($)	Sep. 27, 2019 USD ($)	Sep. 28, 2018 USD ($)
Related Party Transaction [Line Items]
(Loss) Income from equity method investments					$ (300,000)	$ (3,200,000)
dpiX Holding \| Varian
Related Party Transaction [Line Items]
Equity method investment, ownership percentage		40.00%			40.00%
Number of consortium members \| member		4			4
(Loss) Income from equity method investments		$ 30,000.00	$ 3,800,000		$ (700,000)	3,100,000
Equity method investments		48,200,000			48,200,000			$ 48,900,000
Purchases from related party		1,400,000	$ 5,400,000		4,200,000	$ 12,000,000
Accounts payable, related parties		$ 3,400,000			$ 3,400,000			$ 3,700,000
Percentage of manufacturing capacity	50.00%
Percentage of fixed costs	50.00%
Scenario, Forecast \| Fixed Cost Commitments \| dpiX Holding \| Varian
Related Party Transaction [Line Items]
Purchases from related party							$ 14,700,000
Purchases from related party, approved amount remaining				$ 11,000,000