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Significant Accounting Policies - Basis, Estimates and Inv in non-consolidated REITs (Detail)
Dec. 31, 2016
USD ($)
entity
Dec. 31, 2015
entity
Dec. 31, 2014
entity
Significant Accounting Policies      
Number of corporations organized to operate as real estate investment trusts (REITs) | entity 7 9 10
Equity Method Investment Required Balance for Recognition of Distributions Received as Income | $ $ 0    
Number of REITs in which the entity holds non-controlling preferred stock interest | entity 2    
Required investment balance for recognition of distributions received as income | $ $ 0