Accumulated Other Comprehensive Income - Components of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		$ 296,608
Other comprehensive income		1,482
Income taxes	$ (432)	(432)	$ (900)
Ending Balance	319,846	319,846
Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		(563)
Other comprehensive income		(478)
Ending Balance	(1,041)	(1,041)
Debt Security [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		4,350
Other comprehensive income		1,960
Income taxes		(432)
Ending Balance	5,878	5,878
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		3,787
Ending Balance	$ 4,837	$ 4,837

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

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Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.

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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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