Patents (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Accrued Patent Acquisition Related Payments, Current	$ 3,750,000	$ 0
Patents, accumulated amortization	$ 320,236,000	$ 319,580,000
Weighted average useful life of patents and patent rights	4 years
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	5 years