Annual report pursuant to Section 13 and 15(d)

Notes Payable (Details)

v2.4.0.6
Notes Payable (Details) (USD $)
12 Months Ended 1 Months Ended 0 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2012
Unsecured Debt [Member]
Dec. 31, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 5.23% [Member]
Dec. 31, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 5.34% [Member]
Dec. 31, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 5.359% [Member]
Dec. 31, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 5.49% [Member]
Dec. 31, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 5.053% [Member]
Sep. 30, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 3.950 % [Member]
Dec. 31, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 3.950 % [Member]
Sep. 30, 2010
Unsecured Debt [Member]
10 Year Unsecured Notes 3.950 % [Member]
Dec. 31, 2012
Unsecured Debt [Member]
20 Year Unsecured Notes [Member]
May 02, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 5.05 % [Member]
Dec. 31, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 5.05 % [Member]
Apr. 30, 2012
Unsecured Debt [Member]
10 Year Unsecured Notes 5.05 % [Member]
Debt Instrument [Line Items]                                
Coupon stated rate   3.875%     5.125% 5.25% 5.35% 5.35% 4.95%   3.95% 3.95% 7.25%   5.05% 5.05%
Effective rate         5.227% [1] 5.339% [1] 5.359% [1] 5.49% [1] 5.053% [1]   4.018% [1]   7.36% [1]      
Total principal $ 346,519,000     $ 910,000,000                        
Net unamortized discount       (3,810,000)                        
Notes Payable 906,190,000 657,470,000   910,000,000 60,000,000 100,000,000 50,000,000 100,000,000 250,000,000   300,000,000   50,000,000      
Debt Instrument, Face Amount                       300,000,000        
Debt Instrument, Issuance Price, Percentage                       99.438%        
Proceeds from notes payable                   296,400,000            
Repayments of unsecured debt $ 50,000,000 $ 96,521,000 $ 193,799,000                     $ 50,000,000    
[1] Yield on issuance date, including the effects of discounts on the notes.