Balance Sheet Components (Details) - Cash equivalents and short-term investments - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Balance Sheet Components (Details) - Cash equivalents and short-term investments [Line Items]
Amortized Cost	$ 14	$ 2,607
Gross Unrecognized Gains
Gross Unrecognized Losses
Estimated Fair Value	14	2,607
Carrying Value	14	2,607
Corporate Bonds [Member]
Balance Sheet Components (Details) - Cash equivalents and short-term investments [Line Items]
Amortized Cost		1,415
Gross Unrecognized Gains
Gross Unrecognized Losses
Estimated Fair Value		1,415
Carrying Value		1,415
Short-term Investments [Member]
Balance Sheet Components (Details) - Cash equivalents and short-term investments [Line Items]
Amortized Cost		1,415
Gross Unrecognized Gains
Gross Unrecognized Losses
Estimated Fair Value		1,415
Carrying Value		1,415
Money Market Funds [Member]
Balance Sheet Components (Details) - Cash equivalents and short-term investments [Line Items]
Amortized Cost	14	1,192
Gross Unrecognized Gains
Gross Unrecognized Losses
Estimated Fair Value	14	1,192
Carrying Value	14	1,192
Cash Equivalents [Member]
Balance Sheet Components (Details) - Cash equivalents and short-term investments [Line Items]
Amortized Cost	14	1,192
Gross Unrecognized Gains
Gross Unrecognized Losses
Estimated Fair Value	14	1,192
Carrying Value	$ 14	$ 1,192

Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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