Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category Short-Term and Long-Term Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 196,823	$ 129,600
Investments, Gross Unrealized Gains	51	16
Investments, Gross Unrealized (Losses)	(32)	(22)
Investments, Estimated Fair Value	196,842	129,594
Short-Term Investments [Member] \| Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	21,152	20,901
Investments, Gross Unrealized (Losses)		(1)
Investments, Estimated Fair Value	21,152	20,900
Short-Term Investments [Member] \| Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	266	82
Investments, Estimated Fair Value	266	82
Short-Term Investments [Member] \| Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	1,446
Investments, Estimated Fair Value	1,446
Short-Term Investments [Member] \| Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	75,448	24,029
Investments, Gross Unrealized Gains	9	2
Investments, Gross Unrealized (Losses)	(24)	(11)
Investments, Estimated Fair Value	75,433	24,020
Short-Term Investments [Member] \| Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	4,953	2,100
Investments, Gross Unrealized Gains	6
Investments, Gross Unrealized (Losses)		(1)
Investments, Estimated Fair Value	4,959	2,099
Short-Term Investments [Member] \| U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	93,558	82,488
Investments, Gross Unrealized Gains	36	14
Investments, Gross Unrealized (Losses)	(8)	(9)
Investments, Estimated Fair Value	93,586	82,493
Long-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	241,021	157,489
Investments, Gross Unrealized Gains	140	8
Investments, Gross Unrealized (Losses)	(253)	(296)
Investments, Estimated Fair Value	240,908	157,201
Long-Term Investments [Member] \| Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost		48
Investments, Estimated Fair Value		48
Long-Term Investments [Member] \| Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	134,914	75,778
Investments, Gross Unrealized Gains	71	5
Investments, Gross Unrealized (Losses)	(68)	(109)
Investments, Estimated Fair Value	134,917	75,674
Long-Term Investments [Member] \| Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	94,131	64,842
Investments, Gross Unrealized Gains	39	1
Investments, Gross Unrealized (Losses)	(180)	(174)
Investments, Estimated Fair Value	93,990	64,669
Long-Term Investments [Member] \| Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	3,400	1,258
Investments, Gross Unrealized Gains	27
Investments, Gross Unrealized (Losses)	(5)	(4)
Investments, Estimated Fair Value	3,422	1,254
Long-Term Investments [Member] \| U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	8,576	15,563
Investments, Gross Unrealized Gains	3	2
Investments, Gross Unrealized (Losses)		(9)
Investments, Estimated Fair Value	$ 8,579	$ 15,556

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

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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.

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-Publisher FASB

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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

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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