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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 148,965	$ 189,538
Investments, Gross Unrealized Gains	131	35
Investments, Gross Unrealized (Losses)	(80)	(110)
Investments, Estimated Fair Value	149,016	189,463
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	13,530	23,818
Investments, Estimated Fair Value	13,530	23,818
Bankers Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	1,934	1,439
Investments, Estimated Fair Value	1,934	1,439
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	32,655	36,847
Investments, Gross Unrealized Gains	13	6
Investments, Gross Unrealized (Losses)	(36)	(44)
Investments, Estimated Fair Value	32,632	36,809
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	11,664	24,423
Investments, Gross Unrealized (Losses)	(35)	(42)
Investments, Estimated Fair Value	11,629	24,381
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	46,915	46,700
Investments, Gross Unrealized Gains	81	21
Investments, Gross Unrealized (Losses)	(6)	(14)
Investments, Estimated Fair Value	46,990	46,707
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	250	591
Investments, Estimated Fair Value	250	591
Promissory Note [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	675	675
Investments, Estimated Fair Value	675	675
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	16,905	25,414
Investments, Gross Unrealized Gains	23
Investments, Estimated Fair Value	16,928	25,414
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	24,437	29,631
Investments, Gross Unrealized Gains	14	8
Investments, Gross Unrealized (Losses)	(3)	(10)
Investments, Estimated Fair Value	24,448	29,629
Group Insurance Contracts [Member] | Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	6,888	6,276
Investments, Gross Unrealized (Losses)	(859)	(718)
Investments, Estimated Fair Value	$ 6,029	$ 5,558

X

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Section 50
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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

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-Topic 320
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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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-Publisher FASB
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