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Cash, Cash Equivalents, and Available-For-Sale Investments - Portfolio of Available-for-Sale Investments Reported as Short-Term and Long-Term Investments by Contractual Maturity (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Less than one year $ 251,757 $ 213,386
Greater than one year but less than two years   186,238
Total available-for-sale investments $ 251,757 $ 399,624