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Cash, Cash Equivalents and Investments - Amortized Cost to Fair Value (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 570,273
Gross Unrealized Gains	159
Gross Unrealized Losses	(1,818)
Fair Value, Total	568,614
Euro liquidity fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	47,730
Euro liquidity fund [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	47,667
Gross Unrealized Gains	63
Gross Unrealized Losses	0
Fair Value, Total	47,730
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	230,951
Corporate Bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	54,420
Gross Unrealized Gains	22
Gross Unrealized Losses	(66)
Fair Value, Total	54,376
Corporate Bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	177,748
Gross Unrealized Gains	50
Gross Unrealized Losses	(1,223)
Fair Value, Total	176,575
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	9,158
Agency Bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	979
Gross Unrealized Gains	0
Gross Unrealized Losses	(1)
Fair Value, Total	978
Agency Bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,199
Gross Unrealized Gains	0
Gross Unrealized Losses	(19)
Fair Value, Total	8,180
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	86,576
Asset-Backed Securities [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	62,101
Gross Unrealized Gains	0
Gross Unrealized Losses	(107)
Fair Value, Total	61,994
Asset-Backed Securities [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,633
Gross Unrealized Gains	2
Gross Unrealized Losses	(53)
Fair Value, Total	24,582
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	5,459
Municipal Bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	590
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value, Total	590
Municipal Bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,849
Gross Unrealized Gains	20
Gross Unrealized Losses	0
Fair Value, Total	4,869
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	153,797
Treasury Bills [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	109,462
Gross Unrealized Gains	2
Gross Unrealized Losses	(104)
Fair Value, Total	109,360
Treasury Bills [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	44,585
Gross Unrealized Gains	0
Gross Unrealized Losses	(148)
Fair Value, Total	44,437
Sovereign Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	34,943
Sovereign Bonds [Member] | Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,466
Gross Unrealized Gains	0
Gross Unrealized Losses	(26)
Fair Value, Total	21,440
Sovereign Bonds [Member] | Long-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,574
Gross Unrealized Gains	0
Gross Unrealized Losses	(71)
Fair Value, Total	$ 13,503

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