Cash Equivalents and Investments - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Fair Value, Inputs, Level 2	Dec. 31, 2012 Fair Value, Inputs, Level 2
Schedule Of Investments [Line Items]
Impairment losses on marketable securities	$ 0	$ 0
Investments in marketable securities in an excess of 12 months	0
Time deposits at fair value			$ 11,900,000	$ 14,700,000

The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

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Any certificate of deposit or savings account held by a bank or other financial institution for a short-term specified period of time. Because of their short-term, time deposits are considered 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. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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