Organization - Narrative (Details)
3 Months Ended
Mar. 31, 2015
USD ($)
Property
shares
Mar. 31, 2015
USD ($)
Property
shares
Dec. 31, 2014
USD ($)
Property
shares
Summary Of Business And Significant Accounting Policies [Line Items]      
Gross investment in real estate properties $ 8,224,762,000 $ 8,224,762,000 $ 8,043,497,000
Number of real estate properties | Property 2,547 2,547 2,509
Number of shares sold (in shares) | shares 418,401,109 418,401,109 411,350,440
Revenues   $ 200,000  
Number of properties sold | Property   15  
Gross sales proceeds from sale of real estate   $ 77,200,000  
Current Year Acquisitions      
Summary Of Business And Significant Accounting Policies [Line Items]      
Gross investment in real estate properties $ 265,500,000 $ 265,500,000  
Number of properties acquired | Property   53  
Unsecured Debt      
Summary Of Business And Significant Accounting Policies [Line Items]      
Line of credit facility maximum borrowing capacity 600,000,000.0 $ 600,000,000.0  
Maximum borrowing capacity increase, accordion feature 1,000,000,000.0 1,000,000,000.0  
Revolving Credit Facility      
Summary Of Business And Significant Accounting Policies [Line Items]      
Line of credit facility maximum borrowing capacity $ 400,000,000.0 $ 400,000,000.0  
ATM Program      
Summary Of Business And Significant Accounting Policies [Line Items]      
Number of shares sold (in shares) | shares 6,600,000 6,600,000  
Aggregate gross proceeds from issuance of common stock   $ 79,800,000  
Aggregate net sales proceeds from Issuance of common stock   $ 78,600,000  
General Partner      
Summary Of Business And Significant Accounting Policies [Line Items]      
Percentage ownership of operating partnership   1.00%  
Limited Partner      
Summary Of Business And Significant Accounting Policies [Line Items]      
Percentage ownership of operating partnership   99.00%  
LIBOR | Unsecured Debt      
Summary Of Business And Significant Accounting Policies [Line Items]      
Basis spread on variable rate 1.70%    
Owned Properties      
Summary Of Business And Significant Accounting Policies [Line Items]      
Gross investment in real estate properties $ 8,117,359,000 $ 8,117,359,000 $ 7,934,072,000
Number of real estate properties | Property 2,402 2,402 2,364
Gross investment in real estate, percentage   98.70%  
Number of owned real estate properties | Property 2,402 2,402  
Financed Properties      
Summary Of Business And Significant Accounting Policies [Line Items]      
Gross investment in real estate properties $ 107,403,000 $ 107,403,000 $ 109,425,000
Number of real estate properties | Property 145 145 145
Securing mortgage properties, percentage   1.30%  
Securing mortgage properties | Property 145 145