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Commitments, Contingencies, and Concentrations (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]      
Rental expense under operating leases $ 3.6 $ 3.6 $ 3.6
Concentration risk (as a percentage) No single customer comprises greater than 5% of net revenues.