Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 93,350	$ 73,994
Investments, Gross Unrealized Gains	8	7
Investments, Gross Unrealized (Losses)	(373)	(175)
Investments, Estimated Fair Value	92,985	73,826
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5,261	102
Investments, Gross Unrealized Gains	1
Investments, Estimated Fair Value	5,262	102
Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	3,833	989
Investments, Estimated Fair Value	3,833	989
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost		9,121
Investments, Gross Unrealized Gains		1
Investments, Gross Unrealized (Losses)		(9)
Investments, Estimated Fair Value		9,113
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	60,526	19,504
Investments, Gross Unrealized (Losses)	(372)	(145)
Investments, Estimated Fair Value	60,154	19,359
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	8,218	9,367
Investments, Gross Unrealized Gains	1
Investments, Gross Unrealized (Losses)		(15)
Investments, Estimated Fair Value	8,219	9,352
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost		13,294
Investments, Gross Unrealized Gains		4
Investments, Estimated Fair Value		13,298
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	15,512	21,617
Investments, Gross Unrealized Gains	6	2
Investments, Gross Unrealized (Losses)	(1)	(6)
Investments, Estimated Fair Value	15,517	21,613
Group Insurance Contracts [Member] \| Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5,567	5,546
Investments, Gross Unrealized Gains	434	344
Investments, Gross Unrealized (Losses)	0
Investments, Estimated Fair Value	$ 6,001	$ 5,890

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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