Short-term Investments - Fair Values of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Maturing in one year or less	$ 28,726	$ 51,235
Maturing in one to three years	0	3,767
Total available-for-sale securities	$ 28,726	$ 55,002

Amount of debt 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

-Subparagraph (b)

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

-Publisher FASB

-Name Accounting Standards Codification

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Balance Type:	debit
Period Type:	instant