Summary of Continuous Unrealized Loss on Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Schedule Of Held To Maturity Securities [Line Items]
Estimated Fair Value, Less Than 12 Months	$ 102,612
Unrealized Loss, Less Than 12 Months	(91)
Estimated Fair Value, 12 Months or Greater	0
Unrealized Loss, 12 Months or Greater	0
Estimated Fair Value, Total	102,612
Unrealized Loss, Total	(91)
Commercial Paper
Schedule Of Held To Maturity Securities [Line Items]
Estimated Fair Value, Less Than 12 Months	38,055
Unrealized Loss, Less Than 12 Months	(26)
Estimated Fair Value, 12 Months or Greater	0
Unrealized Loss, 12 Months or Greater	0
Estimated Fair Value, Total	38,055
Unrealized Loss, Total	(26)
Corporate Bonds
Schedule Of Held To Maturity Securities [Line Items]
Estimated Fair Value, Less Than 12 Months	64,557
Unrealized Loss, Less Than 12 Months	(65)
Estimated Fair Value, 12 Months or Greater	0
Unrealized Loss, 12 Months or Greater	0
Estimated Fair Value, Total	64,557
Unrealized Loss, Total	$ (65)

Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for twelve months or longer.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity in a continuous loss position.

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This item represents the fair value of securities categorized as held-to-maturity which are in an unrealized loss position.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for less than twelve months.

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This item represents the fair value of securities categorized as held-to-maturity that have been in a continuous unrealized loss position for less than twelve months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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This item represents the fair value of securities categorized as held-to-maturity securities that have been in a continuous unrealized loss position for twelve months or longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

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