Short-Term Investments - Maturities of Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Less than one year	$ 30,946	$ 55,278
Due in 1 - 2 years	901	24,974
Total short-term investments, Estimated Fair Value	$ 31,847	$ 80,252

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

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

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