Cash Equivalents and Investments Classified as Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Cost	$ 390,945	$ 371,370
Unrealized Gain	31	12
Unrealized (Loss)	(122)	(251)
Estimated Fair Value	390,854	371,131
Money market funds
Schedule Of Available For Sale Securities [Line Items]
Cost	20,483	24,915
Estimated Fair Value	20,483	24,915
Corporate notes and commercial paper
Schedule Of Available For Sale Securities [Line Items]
Cost	214,666	226,209
Unrealized Gain	5	8
Unrealized (Loss)	(105)	(170)
Estimated Fair Value	214,566	226,047
U.S. government agency securities
Schedule Of Available For Sale Securities [Line Items]
Cost	155,796	120,246
Unrealized Gain	26	4
Unrealized (Loss)	(17)	(81)
Estimated Fair Value	155,805	120,169
Cash equivalents
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	52,167	36,342
Short-term investments
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	332,596	251,759
Long-term investments
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	$ 6,091	$ 83,030

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

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-Publisher FASB

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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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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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