Quarterly report pursuant to Section 13 or 15(d)

Unsecured Lines of Credit Payable (Details)

v2.4.0.8
Unsecured Lines of Credit Payable (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 3 Months Ended
Sep. 30, 2013
Credit Facility No. 1 [Member]
Dec. 31, 2012
Credit Facility No. 1 [Member]
Sep. 30, 2013
Credit Facility No. 2 [Member]
Dec. 31, 2012
Credit Facility No. 2 [Member]
Sep. 30, 2013
Maximum [Member]
Credit Facility No. 1 [Member]
Sep. 30, 2013
Maximum [Member]
Credit Facility No. 2 [Member]
Mar. 15, 2013
5.125% unsecured notes [Member]
Unsecured Debt [Member]
Line of Credit Facility [Line Items]              
Expiration date Jun. 30, 2015   Jul. 31, 2016        
Committed capacity $ 100,000   $ 400,000   $ 200,000 $ 600,000  
Borrowings outstanding (25,000) 0 (60,000) 0      
Unused and available 75,000   340,000        
Line of Credit Facility [Roll Forward]              
Balance at December 31, 2012   0   0      
Borrowings 50,000   60,000        
Repayments (25,000)   0        
Balance at September 30, 2013 $ 25,000 $ 0 $ 60,000 $ 0      
Interest rate, stated percentage             5.125%