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Stockholders' Equity - Summary of Stock Appreciation Rights Activity (Parenthetical) (Detail) (Stock appreciation rights [Member], USD $)
Dec. 31, 2014
Stock appreciation rights [Member]
  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Closing stock price of common stock $ 99.61us-gaap_SharePrice
/ us-gaap_AwardTypeAxis
= us-gaap_StockAppreciationRightsSARSMember