Summary of Held-to-Maturity Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 113,223us-gaap_HeldToMaturitySecurities
Unrealized Gains	3
Unrealized Losses	(91)
Estimated Fair Value	113,135
Commercial Paper \| Short Term Investments
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	38,081
Unrealized Losses	(26)
Estimated Fair Value	38,055
Corporate Bonds \| Cash and Cash Equivalents
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	1,882
Unrealized Gains	1
Unrealized Losses	(1)
Estimated Fair Value	1,882
Corporate Bonds \| Short Term Investments
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	73,260
Unrealized Gains	2
Unrealized Losses	(64)
Estimated Fair Value	$ 73,198

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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