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Fair value Measurements - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Interest receivable $ 17,864us-gaap_InterestReceivableCurrent $ 17,587us-gaap_InterestReceivableCurrent