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Equity Based Award Plans Monte Carlo (Details) - Restricted Stock [Member]
6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk free rate minimum   0.02% 0.08%
Risk free rate maximum   0.80% 0.50%
Expected life of options (in years) 3 years 3 years  
AERC [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility minimum   22.30% 18.10%
Expected volatility maximum   24.20% 22.50%
Peer Group [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility minimum   16.90% 14.70%
Expected volatility maximum   24.70% 29.50%