Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Net operating tax loss and capital loss carryforwards	$ 68,672	$ 65,783
Capitalized research and development costs	5,270	2,890
Research and development tax credits	1,659	950
Deferred compensation	46	106
Other accruals and reserves	1,214	1,092
Basis of intangible assets	3,870	4,197
Total deferred tax asset	80,731	75,018
Less valuation allowance	(80,731)	(75,018)
Net deferred tax asset	$ 0	$ 0