Summary of Significant Accounting Policies - Components of Other Non-Operating Income (Expense) Recognized in Condensed Consolidated Financial Statements (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Nonoperating Income Expense [Abstract]
Interest Income	$ 151	$ 17	$ 292	$ 30
Foreign currency gains (losses), net	(303)	(170)	(1,032)	396
Gain on sale of a private company investment	0	0	999	6,750
Loss on debt extinguishment	0	0	0	(194)
Other income (expense), net	(67)	927	(127)	968
Other non-operating income (expense), net	$ (219)	$ 774	$ 132	$ 7,950

Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.

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The difference between the carrying value and the sale price of an investment. A gain would be recognized when the sale price of the investment is greater than the carrying value of the investment. This element refers to the Gain included in earnings and not to the cash proceeds of the sale.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business).

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Amount of income (expense) related to nonoperating activities, classified as other.

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