Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Less: accumulated amortization	$ (18,804,000)	$ (18,052,000)
Intangible assets, net	7,748,000	0
Amortization expense	752,000	0	$ 0
Future amortization costs	$ 2,100,000
Amortization period	3 years 9 months
Patents
Finite-Lived Intangible Assets [Line Items]
Patents	$ 26,552,000	$ 18,052,000