Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 189,538	$ 431,382
Investments, Gross Unrealized Gains	35	21
Investments, Gross Unrealized (Losses)	(110)	(740)
Investments, Estimated Fair Value	189,463	430,663
Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	10,576
Investments, Gross Unrealized (Losses)	(718)
Investments, Estimated Fair Value	9,858
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	23,818	11,893
Investments, Gross Unrealized (Losses)		(1)
Investments, Estimated Fair Value	23,818	11,892
Bankers Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	1,439	728
Investments, Estimated Fair Value	1,439	728
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	36,847	125,271
Investments, Gross Unrealized Gains	6
Investments, Gross Unrealized (Losses)	(44)	(274)
Investments, Estimated Fair Value	36,809	124,997
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	24,423
Investments, Gross Unrealized (Losses)	(42)
Investments, Estimated Fair Value	24,381
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	46,700	165,445
Investments, Gross Unrealized Gains	21	5
Investments, Gross Unrealized (Losses)	(14)	(341)
Investments, Estimated Fair Value	46,707	165,109
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	591	8,346
Investments, Gross Unrealized Gains		13
Investments, Gross Unrealized (Losses)		(4)
Investments, Estimated Fair Value	591	8,355
Promissory Note [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	675
Investments, Estimated Fair Value	675
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	25,414
Investments, Estimated Fair Value	25,414
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	29,631	119,699
Investments, Gross Unrealized Gains	8	3
Investments, Gross Unrealized (Losses)	(10)	(120)
Investments, Estimated Fair Value	29,629	$ 119,582
Group Insurance Contracts [Member] \| Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	6,276
Investments, Gross Unrealized (Losses)	(718)
Investments, Estimated Fair Value	5,558
Minority Interest in Private Company [Member] \| Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	4,300
Investments, Estimated Fair Value	$ 4,300

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

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
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

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