Income Taxes - Components of Income (Loss) from Continuing Operations Before Income Tax (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
United States	$ (9,100)	$ (11,382)	$ (16,848)
Loss from continuing operations before income taxes	$ (9,100)	$ (11,382)	$ (16,848)

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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