Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Net operating tax loss and capital loss carryforwards	$ 25,549	$ 23,463
Capitalized research and development costs	4,194	4,620
Research and development tax credits	1,937	1,923
Other accruals and reserves	494	721
Basis of intangible assets	3,136	3,658
Total deferred tax asset	35,310	34,385
Less valuation allowance	(35,310)	(34,385)
Net deferred tax asset	$ 0	$ 0