Properties, net (Details 2) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Properties    
Projects in development or held for future development $ 489,618 $ 545,426
Assets held for sale, net 0 14,339
Greater Baltimore    
Properties    
Number of properties held-for-sale   2
Assets held for sale, net   14,300
Projects in development or held for future development | Land in development or held for future development    
Properties    
Projects in development or held for future development 219,852 214,977
Projects in development or held for future development | Construction in progress, excluding land    
Properties    
Projects in development or held for future development $ 269,766 $ 330,449