Business Combinations - Additional Information (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]
Total net sales					$ 1,798,539	$ 1,339,202
Net income					$ 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]
Total cash payments to Rofin shareholders and option holders	$ 47,400
Expensed 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
Rofin-Sinar
Business Acquisition [Line Items]
Cash consideration to Rofin's shareholders		$ 904,491
Cash settlement paid for Rofin employee stock options		15,290
Total cash payments to Rofin shareholders and option holders		919,781
Add: fair value of previously owned Rofin shares		20,685
Less: post-merger stock compensation expense		(4,152)
Total purchase price to allocate		$ 936,314
Business acquisition, share price (dollars per share)		$ 32.50
Total estimated merger consideration for canceled of options held by Rofin employees			$ 11,100
Remeasurement gain			$ 5,400
Acquired finished goods and work in process amortization period			6 months
Expensed acquisition-related costs					$ 17,600
Net sales					434,900
Net loss from acquired business					48,100
Rofin-Sinar | Inventories
Business Acquisition [Line Items]
Assets fair value adjustment			$ 26,400
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 | Backlog
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			6 months
Rofin-Sinar | Trademarks
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			3 years
Rofin-Sinar | Minimum
Business Acquisition [Line Items]
The fair value write-up of acquired PPE, amortization period			3 years
Rofin-Sinar | Minimum | Existing technology
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			3 years
Rofin-Sinar | Minimum | Customer relationships
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			5 years
Rofin-Sinar | Maximum
Business Acquisition [Line Items]
The fair value write-up of acquired PPE, amortization period			31 years
Rofin-Sinar | Maximum | Patents [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			5 years
Rofin-Sinar | Maximum | Customer relationships
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			10 years