Annual report pursuant to Section 13 and 15(d)

Notes Payable (Details)

v2.4.0.6
Notes Payable (Details) (USD $)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Debt Instrument [Line Items]      
Coupon stated rate 3.875%    
Total principal $ 432,185,000    
Net unamortized discount (2,530,000)    
Repayments of Unsecured Debt 96,521,000 193,799,000 197,414,000
2012 27,000,000    
2013 87,580,000    
2014 3,724,000    
2015 22,390,000    
2016 134,943,000    
Thereafter 156,548,000    
Notes Payable 657,470,000 753,587,000  
Unsecured Debt [Member]
     
Debt Instrument [Line Items]      
Total principal 660,000,000    
2012 50,000,000    
2013 60,000,000    
2014 100,000,000    
2015 150,000,000    
2016 0    
Thereafter 300,000,000    
Notes Payable 660,000,000    
Unsecured Debt [Member] | 10 Year Unsecured Notes 5.064% [Member]
     
Debt Instrument [Line Items]      
Coupon stated rate 5.05%    
Effective rate 5.064% [1]    
Notes Payable 50,000,000    
Unsecured Debt [Member] | 10 Year Unsecured Notes 5.23% [Member]
     
Debt Instrument [Line Items]      
Coupon stated rate 5.125%    
Effective rate 5.23% [1]    
Notes Payable 60,000,000    
Unsecured Debt [Member] | 10 Year Unsecured Notes 5.34% [Member]
     
Debt Instrument [Line Items]      
Coupon stated rate 5.25%    
Effective rate 5.34% [1]    
Notes Payable 100,000,000    
Unsecured Debt [Member] | 10 Year Unsecured Notes 5.359% [Member]
     
Debt Instrument [Line Items]      
Coupon stated rate 5.35%    
Effective rate 5.359% [1]    
Notes Payable 50,000,000    
Unsecured Debt [Member] | 10 Year Unsecured Notes 5.49% [Member]
     
Debt Instrument [Line Items]      
Coupon stated rate 5.35%    
Effective rate 5.49% [1]    
Notes Payable 100,000,000    
Unsecured Debt [Member] | 10 Year Unsecured Notes 5.053% [Member]
     
Debt Instrument [Line Items]      
Coupon stated rate 4.95%    
Effective rate 5.053% [1]    
Notes Payable 250,000,000    
Unsecured Debt [Member] | 20 Year Unsecured Notes [Member]
     
Debt Instrument [Line Items]      
Coupon stated rate 7.25%    
Effective rate 7.36% [1]    
Notes Payable 50,000,000    
Unsecured Debt [Member] | 5.95% Unsecured Notes [Member]
     
Debt Instrument [Line Items]      
Coupon stated rate 5.95%    
Repayments of Unsecured Debt 93,900,000    
Convertible Notes Payable [Member] | 3.875% Convertible Notes [Member]
     
Debt Instrument [Line Items]      
Coupon stated rate 3.875%    
Repayments of notes payable $ 2,700,000    
[1] Yield on issuance date, including the effects of discounts on the notes.