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Fair Values of Financial Instruments - Additional Information (Detail)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
4.97% Series A Senior Notes, Due October 5th 2020
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current market rates used in measuring fair value 4.52% 3.36%
4.27% Series B Senior Notes, Due June 14th 2022
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Current market rates used in measuring fair value 4.89% 3.70%