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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Significant Accounting Policies [Line Items]      
Prior period reclassification adjustment   $ 2.7 $ 2.7
Bad debt expenses $ 0.2    
REIT taxable income distributed to stockholders 100.00%    
Minimum
     
Significant Accounting Policies [Line Items]      
Minimum REIT taxable income distributed to stockholders 90.00%