Quarterly report pursuant to Section 13 or 15(d)

Unsecured Lines of Credit Payable (Details)

v2.4.0.6
Unsecured Lines of Credit Payable (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Credit Facility No. 1 [Member]
Mar. 31, 2013
Credit Facility No. 2 [Member]
Mar. 31, 2013
Maximum [Member]
Credit Facility No. 1 [Member]
Mar. 31, 2013
Maximum [Member]
Credit Facility No. 2 [Member]
Mar. 31, 2013
5.125% unsecured notes [Member]
Unsecured Debt [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 (10,000) (60,000)        
Unused and available 90,000 340,000        
Line of Credit Facility [Roll Forward]            
Balance at December 31, 2012 0 0        
Borrowings 25,000 60,000        
Repayments (15,000) 0        
Balance at March 31, 2013 $ 10,000 $ 60,000        
Interest rate, stated percentage         5.125% 5.125%