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Incentive Plan - Summary of Fair Value of Stock Options Granted (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Risk-free interest rate 1.47% 1.40% 3.08%
Expected option life 7 years 7 years 7 years
Expected volatility 29.00% 29.00% 29.00%
Expected dividend yield 3.27% 3.47% 3.46%
Weighted average fair value of an option share granted during the year $ 3.01 $ 2.69 $ 3.14
Intrinsic value of options exercised during the year $ 11 $ 106 $ 10