Fair Value Disclosures - Cash Equivalents, as Well as Hierarchy for Financial Instruments Measured at Fair Value on Recurring Basis (Detail) (Money market funds [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 209,245	$ 189,092
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 209,245	$ 189,092