Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 37,761	$ 55,608
Research and development and other credits	5,288	6,548
Patents and licenses	1,080	910
Equity method investments at fair value	(7,848)	(23,946)
Stock options	2,062	713
Other, net	174	812
Total	38,517	40,645
Valuation allowance	(38,517)	(40,645)
Net deferred tax assets