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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 89,204	$ 73,994
Investments, Gross Unrealized Gains	6	7
Investments, Gross Unrealized (Losses)	(363)	(175)
Investments, Estimated Fair Value	88,847	73,826
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	6,261	102
Investments, Gross Unrealized Gains	1
Investments, Estimated Fair Value	6,262	102
Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	4,540	989
Investments, Estimated Fair Value	4,540	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	45,342	19,504
Investments, Gross Unrealized (Losses)	(361)	(145)
Investments, Estimated Fair Value	44,981	19,359
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost		9,367
Investments, Gross Unrealized (Losses)		(15)
Investments, Estimated Fair Value		9,352
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	3,601	13,294
Investments, Gross Unrealized Gains	1	4
Investments, Estimated Fair Value	3,602	13,298
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	29,460	21,617
Investments, Gross Unrealized Gains	4	2
Investments, Gross Unrealized (Losses)	(2)	(6)
Investments, Estimated Fair Value	29,462	21,613
Group Insurance Contracts [Member] | Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5,329	5,546
Investments, Gross Unrealized Gains	417	344
Investments, Estimated Fair Value	$ 5,746	$ 5,890

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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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