Fair Value Of Financial Instruments - Measurement of Asset and Liabilities at Fair Value on Recurring Basis (Detail) (USD $) | Jun. 30, 2014 | Dec. 31, 2013 |
In Thousands, unless otherwise specified |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | $258,948 | $265,625 |
Strategic investments | 500 | ' |
Assets | 259,448 | 265,625 |
Fair value measurements, recurring | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 60,002 | 65,700 |
Strategic investments | 500 | 0 |
Fair value measurements, recurring | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 60,002 | 65,700 |
Strategic investments | 0 | 0 |
Assets | 60,002 | 65,700 |
Fair value measurements, recurring | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 0 | 0 |
Strategic investments | 0 | 0 |
Assets | 198,946 | 199,925 |
Fair value measurements, recurring | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Cash equivalents | 0 | 0 |
Strategic investments | 500 | 0 |
Assets | 500 | 0 |
Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 68,950 | 78,609 |
Corporate bonds | Fair value measurements, recurring | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 68,950 | 78,609 |
Corporate bonds | Fair value measurements, recurring | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 0 | 0 |
Corporate bonds | Fair value measurements, recurring | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 68,950 | 78,609 |
Corporate bonds | Fair value measurements, recurring | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 0 | 0 |
Agency bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 112,999 | 121,316 |
Agency bonds | Fair value measurements, recurring | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 112,999 | 121,316 |
Agency bonds | Fair value measurements, recurring | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 0 | 0 |
Agency bonds | Fair value measurements, recurring | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 112,999 | 121,316 |
Agency bonds | Fair value measurements, recurring | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 0 | 0 |
U.S. treasury securities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 12,005 | ' |
U.S. treasury securities | Fair value measurements, recurring | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 12,005 | 0 |
U.S. treasury securities | Fair value measurements, recurring | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 0 | 0 |
U.S. treasury securities | Fair value measurements, recurring | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 12,005 | 0 |
U.S. treasury securities | Fair value measurements, recurring | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 0 | 0 |
Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 4,992 | ' |
Commercial paper | Fair value measurements, recurring | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 4,992 | 0 |
Commercial paper | Fair value measurements, recurring | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 0 | 0 |
Commercial paper | Fair value measurements, recurring | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | 4,992 | 0 |
Commercial paper | Fair value measurements, recurring | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] | ' | ' |
Available-for-sale securities | $0 | $0 |