Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash	$ 500	$ 499
Money market funds	140,406	155,814
Accrued Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Treasury lock		48,829
Quoted prices in active markets for identical assets (Level 1) | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash	500	499
Money market funds	140,406	155,814
Other observable inputs (Level 2) | Accrued Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Treasury lock		$ 48,829