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Intangible Assets (Tables)
 12 Months Ended
Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]  
Schedule of patents and intangible assets
The components of these intangible assets are as follows:
 
As of December 31,
 
2017
 
2016
 
(in thousands)
Patents
$
26,552

 
$
18,052

Less accumulated amortization
(18,804
)
 
(18,052
)
 
 
 
Intangible assets, net
7,748

 
$
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