Short-Term Investments - Maturities of Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investment Securities [Line Items]
Less than one year	$ 76,779	$ 43,470
Due in 1 - 2 years	27,727	27,384
Total short-term investments, Estimated Fair Value	$ 104,506	$ 70,854

Amount of debt securities categorized neither as held-to-maturity nor trading.

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