Quarterly report pursuant to Section 13 or 15(d)

Mortgage Notes Payable and Line of Credit - Additional Information (Detail)

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Mortgage Notes Payable and Line of Credit - Additional Information (Detail) (USD $)
 9 Months Ended 1 Months Ended 1 Months Ended
Sep. 30, 2013
Mortgages
Property
Dec. 31, 2012
Aug. 31, 2013
Senior Unsecured Revolving Credit Facility [Member]
Sep. 30, 2013
Senior Unsecured Revolving Credit Facility [Member]
Aug. 31, 2013
Senior Secured Revolving Credit Facility [Member]
Aug. 31, 2013
Senior Secured Revolving Credit Facility [Member]
Prior Line of Credit Facility [Member]
Sep. 30, 2013
Letter of Credit [Member]
Sep. 30, 2013
Mortgage Notes Payable [Member]
Mortgages
Proforma Debt Instrument [Line Items]                
Number of fixed-rate mortgage notes payable               34
Weighted average interest rate on all debt outstanding 5.36%             5.50%
Number of properties collateralized in fixed-rate mortgage notes payable 68              
Number of long-term mortgages issued 4              
Fair value of fixed-rate mortgage notes payable outstanding $ 409,800,000              
Carrying value of fixed-rate mortgage notes payable outstanding 409,762,000 359,185,000            
Line of credit, outstanding     60,000,000 28,900,000 75,000,000      
Line of credit, maturity date     2016-08          
Extension period subject to payment of fee     1 year          
Extension fee on the initial maturity date     0.25%          
Line of credit, maturity date           Dec. 28, 2013    
Standby letters of credit sublimit     20,000,000          
Line of credit facility, maximum additional amount drawn 16,200,000   75,000,000          
Line of credit, variable spread on interest rate     3.25%          
Annual maintenance fee     30,000          
Unused commitment fee     0.25%          
Line of credit covenant limit of distributions to shareholders percentage     100.00%          
Line of credit at an interest rate 3.00%     3.20%        
Letters of credit, outstanding             $ 6,400,000