Revenue From Contracts With Customers (Disaggregation of Revenue, By Product) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total	$ 306,627	$ 329,138	$ 363,769	$ 315,047	$ 330,051	$ 356,346	$ 413,613	$ 359,864	$ 1,314,581	$ 1,459,874	$ 1,408,889
High Power Continuous Wave ("CW") Lasers
Disaggregation of Revenue [Line Items]
Total									734,745	909,726
Medium and Low Power CW Lasers
Disaggregation of Revenue [Line Items]
Total									56,625	95,764
Pulsed Lasers
Disaggregation of Revenue [Line Items]
Total									137,675	162,048
Quasi-Continuous Wave ("QCW") Lasers
Disaggregation of Revenue [Line Items]
Total									56,440	66,700
Laser and Non-Laser Systems
Disaggregation of Revenue [Line Items]
Total									141,647	59,330
Other Revenue including Amplifiers, Service, Parts, Accessories and Change in Deferred Revenue
Disaggregation of Revenue [Line Items]
Total									$ 187,449	$ 166,306