Goodwill and Intangible Assets - Goodwill (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2018 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 417,694
Additions	31,456
Translation adjustments and other	(5,084)
Goodwill, end of period	444,066
OEM Laser Sources
Goodwill [Roll Forward]
Goodwill, beginning of period	102,178
Additions	0
Translation adjustments and other	(1,143)
Goodwill, end of period	101,035
Industrial Lasers & Systems
Goodwill [Roll Forward]
Goodwill, beginning of period	315,516
Additions	31,456
Translation adjustments and other	(3,941)
Goodwill, end of period	$ 343,031