Financial Assets Measured at Fair Value (Detail) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	$ 41,957	$ 24,938
Quoted Prices in Active Markets (Level 1)
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	37,952	15,910
Significant Other Observable Inputs (Level 2)
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	4,005	9,028
Cash Equivalents
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	37,952	15,910
Cash Equivalents | Quoted Prices in Active Markets (Level 1)
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	37,952	15,910
Marketable debt securities
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	4,005	9,028
Marketable debt securities | Significant Other Observable Inputs (Level 2)
Financial Assets Measured at Fair Value [Line Items]
Assets fair value disclosure Recurring	$ 4,005	$ 9,028