Fair Value of Financial Instruments - Financial Instruments Measured at Fair Value on Recurring Basis by Level within Fair Value Hierarchy (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financial Assets
Marketable securities	$ 135,383us-gaap_AvailableForSaleSecurities	$ 164,619us-gaap_AvailableForSaleSecurities
Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	11,366	9,708
Marketable securities	135,383	164,619
Financial Assets Total	146,749	174,327
Financial Liabilities
Derivative liability	98	83
Fair Value, Measurements, Nonrecurring
Financial Liabilities
Financial Liabilities Total		0
Level 1 \| Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	10,603	1,880
Marketable securities	4,839	4,897
Financial Assets Total	15,442	6,777
Financial Liabilities
Derivative liability	0	0
Level 2 \| Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	763	7,828
Marketable securities	130,544	159,722
Financial Assets Total	131,307	167,550
Financial Liabilities
Derivative liability	0	0
Level 3 \| Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	0	0
Marketable securities	0	0
Financial Assets Total	0	0
Financial Liabilities
Derivative liability	$ 98	$ 83

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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-Glossary Cash

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Fair value of financial and nonfinancial obligations.

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