Annual report pursuant to Section 13 and 15(d)

Subsequent Events (Details)

v2.4.0.6
Subsequent Events (Details) (USD $)
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Subsequent Event [Line Items]    
Stock Issued During Period, Shares, New Issues 4,600,000  
Number of Operating Partnership Units Owned by Family Limited Partners 2,872,973  
New Construction [Member]
    
Subsequent Event [Line Items]    
Subsequent Event, Date Feb. 20, 2012  
Estimated Square Footage of Real Estate Property When Completed 328,000  
Parent Company [Member]
    
Subsequent Event [Line Items]    
Partners' Capital Account, Units, Converted 641,328  
Stock Issued During Period, Shares, Conversion of Units 641,328  
Long-term Debt $ 1,025,542,000 $ 714,616,000
Parent Company [Member] | Equity Exchange [Member]
    
Subsequent Event [Line Items]    
Subsequent Event, Date Jan. 01, 2012  
Stock Issued During Period, Shares, Conversion of Units 4,069,008  
Subsidiaries [Member]
    
Subsequent Event [Line Items]    
Partners' Capital Account, Units, Converted 160,332  
Long-term Debt 1,025,542,000 714,616,000
Subsidiaries [Member] | Equity Exchange [Member]
    
Subsequent Event [Line Items]    
Partners' Capital Account, Units, Converted 1,017,252  
Number of Operating Partnership Units Owned by Family Limited Partners 1,855,721  
Subsidiaries [Member] | New Employment Agreement [Member]
    
Subsequent Event [Line Items]    
Stock Issued During Period, Shares, New Issues 45,000  
Subsequent Event, Date Feb. 28, 2012  
Unsecured Term Loan [Member] | Subsidiaries [Member] | Issuance of Debt [Member]
    
Subsequent Event [Line Items]    
Subsequent Event, Date Feb. 24, 2012  
Long-term Debt 250,000,000  
Debt Instrument, Maturity Date, Description 2019  
Debt Instrument, Earliest Prepayment Without Penalty Date 2015  
Debt Instrument, Basis Spread on Variable Rate 1.80%  
Line of Credit Facility, Syndicataed Line, Maximum Borrowings, Included in Total Line of Credit Maximum Borrowings $ 520,000,000  
Service Condition [Member] | Parent Company [Member] | New Employment Agreement [Member]
    
Subsequent Event [Line Items]    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 5  
Service Condition [Member] | Subsidiaries [Member] | New Employment Agreement [Member]
    
Subsequent Event [Line Items]    
Stock Issued During Period, Shares, Restricted Stock Award, Gross 90,000  
Service and Performance Conditions [Member] | Parent Company [Member] | New Employment Agreement [Member]
    
Subsequent Event [Line Items]    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 5  
Service and Performance Conditions [Member] | Subsidiaries [Member] | New Employment Agreement [Member]
    
Subsequent Event [Line Items]    
Stock Issued During Period, Shares, Restricted Stock Award, Gross 90,000