Financial Assets Measured at Fair Value (Detail) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	$ 27,936	$ 34,861
Cash Equivalents
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	18,893	8,825
Marketable Securities
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	9,043	26,036
Quoted Prices in Active Markets (Level 1)
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	18,893	8,825
Quoted Prices in Active Markets (Level 1) | Cash Equivalents
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	18,893	8,825
Significant Other Observable Inputs (Level 2)
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	9,043	26,036
Significant Other Observable Inputs (Level 2) | Marketable Securities
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	$ 9,043	$ 26,036