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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category Short-Term and Long-Term Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 53,088	$ 431,382
Investments, Gross Unrealized Gains	34	21
Investments, Gross Unrealized (Losses)	(18)	(740)
Investments, Estimated Fair Value	53,104	430,663
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	1,395	11,893
Investments, Gross Unrealized (Losses)		(1)
Investments, Estimated Fair Value	1,395	11,892
Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	2,487	728
Investments, Estimated Fair Value	2,487	728
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	18,317	125,271
Investments, Gross Unrealized Gains	13
Investments, Gross Unrealized (Losses)	(4)	(274)
Investments, Estimated Fair Value	18,326	124,997
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	2,794
Investments, Gross Unrealized (Losses)	(1)
Investments, Estimated Fair Value	2,793
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	16,699	165,445
Investments, Gross Unrealized Gains	15	5
Investments, Gross Unrealized (Losses)	(13)	(341)
Investments, Estimated Fair Value	16,701	165,109
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	592	8,346
Investments, Gross Unrealized Gains	1	13
Investments, Gross Unrealized (Losses)		(4)
Investments, Estimated Fair Value	593	8,355
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	1,151
Investments, Gross Unrealized Gains	1
Investments, Estimated Fair Value	1,152
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	9,653	119,699
Investments, Gross Unrealized Gains	4	3
Investments, Gross Unrealized (Losses)		(120)
Investments, Estimated Fair Value	9,657	$ 119,582
Group Insurance Contracts [Member] | Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5,988
Investments, Gross Unrealized (Losses)	(32)
Investments, Estimated Fair Value	$ 5,956

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)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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