Stock-Based Compensation - Stock Compensation Expense (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Nov. 07, 2016	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated stock-based compensation expense		$ 7,549	$ 5,041	$ 20,251	$ 18,075
Capitalized share-based compensation costs		1,200	900	3,500	2,600
Amortization of capitalized share-based compensation expenses		1,200	900	3,200	2,400
Total compensation cost, unvested stock-based awards granted but not yet recognized		43,600		$ 43,600
Total compensation cost, weighted-average period of amortization (in years)				1 year 6 months
Period End
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Capitalized share-based compensation costs				$ 1,500	1,100
Rofin-Sinar
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
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
Cost of sales
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated stock-based compensation expense		1,168	880	3,174	2,618
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated stock-based compensation expense		838	639	2,378	2,289
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated stock-based compensation expense		6,577	5,373	18,517	18,323
Income tax benefit
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Income tax benefit		$ (1,034)	$ (1,851)	$ (3,818)	$ (5,155)