Business Combinations (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended	12 Months Ended
	Mar. 08, 2018	Nov. 07, 2016	Dec. 31, 2016	Sep. 29, 2018	Sep. 30, 2017	Oct. 01, 2016
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Revenue					$ 1,798,539	$ 1,339,202
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Goodwill				$ 442,940	417,694	101,458
Business Acquisition, Pro Forma Net Income (Loss)					$ 233,012	$ 5,813
Pro forma, net income per share: Basic (in dollars per share)					$ 9.52	$ 0.24
Pro forma, net income per share: Diluted (in dollars per share)					$ 9.40	$ 0.24
Minimum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life				3 years
Maximum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life				15 years
O.R. Laser
Business Acquisition [Line Items]
Business acquisition, cash paid for acquired entity	$ 47,400
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Cash, cash equivalents and short-term investments	1,936
Accounts receivable	3,973
Inventory	2,360
Prepaid expenses and other assets	630
Property and equipment	1,515
Liabilities assumed	(5,119)
Deferred tax liabilities	(4,517)
Goodwill	31,456
Total purchase price to allocate	$ 47,384
Business Combination, Acquisition Related Costs				$ 600
O.R. Laser | Minimum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year
O.R. Laser | Maximum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	8 years
O.R. Laser | Existing technology
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets	$ 14,100
O.R. Laser | Non-competition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets	200
O.R. Laser | Backlog
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets	100
O.R. Laser | Customer relationships
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets	700
O.R. Laser | Trademarks
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets	$ 50
Rofin-Sinar
Business Acquisition [Line Items]
Cash consideration to Rofin's shareholders		$ 904,491
Total purchase price to allocate		$ 936,314
Business acquisition, share price (dollars per share)		$ 32.50
Business acquisition, cash paid for acquired entity		$ 919,781
Add: fair value of previously owned Rofin shares		20,685
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Cash, cash equivalents and short-term investments			$ 163,425
Accounts receivable			90,877
Inventory			189,869
Prepaid expenses and other assets			15,362
Assets held for sale, current			29,545
Property and equipment			125,723
Other assets			31,854
Goodwill			298,170
Current portion of long-term obligations			(3,633)
Current liabilities held for sale			(7,001)
Accounts payable			(21,314)
Other current liabilities			(68,242)
Long-term debt			(11,641)
Other long-term liabilities			(122,517)
Total purchase price to allocate			936,314
Business Combination, Acquisition Related Costs					$ 17,600
Cash settlement paid for Rofin employee stock options		15,290
Total estimated merger consideration for canceled of options held by Rofin employees			11,100
Post merger stock compensation expense		$ 4,152
Remeasurement gain			$ 5,400
Acquired finished goods and work in process amortization period			6 months
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual					434,900
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual					(48,100)
Rofin-Sinar | Minimum
Business Acquisition [Line Items]
The fair value write-up of acquired PPE, amortization period			3 years
Rofin-Sinar | Maximum
Business Acquisition [Line Items]
The fair value write-up of acquired PPE, amortization period			31 years
Rofin-Sinar | Inventories
Business Acquisition [Line Items]
Assets fair value adjustment			$ 26,400
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Incremental cost of sales recorded from inventory fair value adjustment					$ 26,400
Rofin-Sinar | Property and equipment
Business Acquisition [Line Items]
Assets fair value adjustment			36,000
Rofin-Sinar | Existing technology
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets			$ 169,029
Rofin-Sinar | Existing technology | Minimum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			3 years
Rofin-Sinar | Patents [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets			$ 300
Rofin-Sinar | Patents [Member] | Maximum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			5 years
Rofin-Sinar | In-process research and development
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets			$ 6,000
Rofin-Sinar | Backlog
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			6 months
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets			$ 5,600
Rofin-Sinar | Customer relationships
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets			$ 39,209
Rofin-Sinar | Customer relationships | Minimum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			5 years
Rofin-Sinar | Customer relationships | Maximum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			10 years
Rofin-Sinar | Trademarks
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			3 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Intangible assets			$ 5,699