Revenue From Contracts With Customers (Disaggregation of Revenue, By Product) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total	$ 330,051	$ 356,346	$ 413,613	$ 359,864	$ 361,055	$ 392,615	$ 369,373	$ 285,846	$ 1,459,874	$ 1,408,889	$ 1,006,173
High Power Continuous Wave ("CW") Lasers
Disaggregation of Revenue [Line Items]
Total									909,726
Medium and Low Power CW Lasers
Disaggregation of Revenue [Line Items]
Total									95,764
Pulsed Lasers
Disaggregation of Revenue [Line Items]
Total									162,048
Quasi-Continuous Wave ("QCW") Lasers
Disaggregation of Revenue [Line Items]
Total									66,700
Laser Systems
Disaggregation of Revenue [Line Items]
Total									59,330
Other Revenue including Amplifiers, Service, Parts, Accessories and Change in Deferred Revenue
Disaggregation of Revenue [Line Items]
Total									$ 166,306