Debt - Revolving Credit Facilities - Narrative (Details) (USD $)
3 Months Ended 0 Months Ended
Mar. 31, 2015
Mar. 31, 2015
Dec. 31, 2014
Line of Credit Facility [Line Items]      
Amount outstanding 181,518,000 $ 181,518,000 $ 12,780,000
Number of properties securing borrowings 145 145  
Weighted Average      
Line of Credit Facility [Line Items]      
Weighted Average Term 5 years 3 months 18 days    
Weighted Average Effective Interest Rates 5.33% 5.33%  
Weighted Average Stated Rates 4.89% 4.89%  
Unsecured Debt      
Line of Credit Facility [Line Items]      
Line of credit facility maximum borrowing capacity 600,000,000.0 600,000,000.0  
Line of credit facility, accordion feature, increase limit 1,000,000,000.0 1,000,000,000.0  
Maximum borrowing capacity increase, accordion feature 1,000,000,000.0 1,000,000,000.0  
Commitment fee on unused capacity   0.15%  
Origination costs   3,500,000  
Amount outstanding 170,000,000 170,000,000  
Line of credit facility remaining borrowing capacity 430,000,000 430,000,000  
Unsecured Debt | Minimum      
Line of Credit Facility [Line Items]      
Commitment fee on unused capacity   0.125%  
Unsecured Debt | Maximum      
Line of Credit Facility [Line Items]      
Commitment fee on unused capacity   0.30%  
Unsecured Debt | Weighted Average      
Line of Credit Facility [Line Items]      
Weighted Average Term 6 years 9 months 18 days    
Weighted Average Effective Interest Rates 9.12% 9.12%  
Weighted Average Stated Rates 7.00% 7.00%  
Unsecured Debt | LIBOR      
Line of Credit Facility [Line Items]      
Basis spread on variable rate   1.70%  
Unsecured Debt | LIBOR | Minimum      
Line of Credit Facility [Line Items]      
Basis spread on variable rate   0.875%  
Unsecured Debt | LIBOR | Maximum      
Line of Credit Facility [Line Items]      
Basis spread on variable rate   1.55%  
Line of Credit      
Line of Credit Facility [Line Items]      
Commitment fee on unused capacity   0.35%  
Debt extinguishment costs   2,000,000  
Line of Credit | LIBOR      
Line of Credit Facility [Line Items]      
Basis spread on variable rate   2.50%  
Revolving Credit Facility      
Line of Credit Facility [Line Items]      
Line of credit facility maximum borrowing capacity 400,000,000.0 400,000,000.0  
Revolving Credit Facility | Special Purpose Entity      
Line of Credit Facility [Line Items]      
Line of credit facility maximum borrowing capacity 40,000,000 40,000,000  
Amount outstanding 15,100,000 15,100,000  
Weighted Average Term 24 months    
Number of separate advances 3 3  
Number of properties securing borrowings 3 3  
Weighted Average Effective Interest Rates 3.89% 3.89%  
Revolving Credit Facility | Weighted Average | Special Purpose Entity      
Line of Credit Facility [Line Items]      
Weighted Average Stated Rates 3.58% 3.58%  
Swingline Loans | Unsecured Debt      
Line of Credit Facility [Line Items]      
Line of credit facility maximum borrowing capacity 50,000,000.0 50,000,000.0  
Letters of Credit | Unsecured Debt      
Line of Credit Facility [Line Items]      
Line of credit facility maximum borrowing capacity 60,000,000.0 $ 60,000,000.0