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Patents (Details) - USD ($)
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]      
Patents, accumulated amortization $ 363,558,000   $ 358,043,000
Weighted average useful life of patents and patent rights 5 years    
Patent portfolio investment costs $ 0 $ 1,000,000  
Minimum [Member]      
Finite-Lived Intangible Assets [Line Items]      
Useful life of patents and patent rights 1 year    
Maximum [Member]      
Finite-Lived Intangible Assets [Line Items]      
Useful life of patents and patent rights 7 years