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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category Short-Term Securities and Long-Term Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 71,338	$ 431,382
Investments, Gross Unrealized Gains	49	21
Investments, Gross Unrealized (Losses)	(14)	(740)
Investments, Estimated Fair Value	71,373	430,663
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	17,358	11,893
Investments, Gross Unrealized (Losses)		(1)
Investments, Estimated Fair Value	17,358	11,892
Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	3,056	728
Investments, Estimated Fair Value	3,056	728
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	14,164	125,271
Investments, Gross Unrealized Gains	16
Investments, Gross Unrealized (Losses)	(7)	(274)
Investments, Estimated Fair Value	14,173	124,997
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	19,454	165,445
Investments, Gross Unrealized Gains	21	5
Investments, Gross Unrealized (Losses)	(7)	(341)
Investments, Estimated Fair Value	19,468	165,109
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	592	8,346
Investments, Gross Unrealized Gains	3	13
Investments, Gross Unrealized (Losses)		(4)
Investments, Estimated Fair Value	595	8,355
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	1,151
Investments, Gross Unrealized Gains	3
Investments, Estimated Fair Value	1,154
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	15,563	119,699
Investments, Gross Unrealized Gains	6	3
Investments, Gross Unrealized (Losses)		(120)
Investments, Estimated Fair Value	15,569	$ 119,582
Group Insurance Contracts [Member] | Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5,938
Investments, Gross Unrealized (Losses)	(8)
Investments, Estimated Fair Value	$ 5,930

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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
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-Name Accounting Standards Codification
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-Section 50
-Paragraph 5
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-Topic 320
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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
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-Section 50
-Paragraph 2
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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