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Equity - Assumptions used to Value the Performance-Vested Restricted Stock Awards (Detail) - Restricted Stock Awards [Member]
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Valuation assumptions:      
Expected volatility 34.00% 33.00% 34.80%
Expected dividend yield 9.40% 4.70% 1.30%
Risk-free interest rate 0.80% 0.70% 0.40%