CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Consolidated Statement Of Comprehensive Income [Abstract]
Net income	$ 7,187	$ 17,369	$ 37,014	$ 33,713
Other comprehensive income:
Change in net unrealized gains (losses) on marketable securities, net of tax	(68)	(2)	62	43
Change in currency translation adjustments	(202)	91	(425)	1,344
Total comprehensive income	$ 6,917	$ 17,458	$ 36,651	$ 35,100

Consolidated Statement of Comprehensive Income [Abstract]

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Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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