Short-term Investments - Summary of Fair Values of Available-for-Sale Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Maturing in one year or less	$ 20,093
Maturing after one year through three years	12,829
Total available-for-sale securities, Fair value	$ 32,922

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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