Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss, Net of Tax (Details) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2017	$ 333,154
Balance at September 30, 2018	374,156
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2017	1,079
Net current period other comprehensive income	425
Reclassifications	0
Balance at September 30, 2018	1,504
Net Unrealized (Gains) Losses on Marketable Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2017	126
Net current period other comprehensive income	(62)
Reclassifications	0
Balance at September 30, 2018	64
Accumulated Other Comprehensive Loss (Income) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2017	1,205
Net current period other comprehensive income	363
Reclassifications	0
Balance at September 30, 2018	$ 1,568

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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