Significant Credit and Revenue Concentration - Narrative (Details)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2015
tenant
Customer
Jun. 30, 2014
Jun. 30, 2015
tenant
Customer
Dec. 31, 2014
tenant
Customer
Revenue, Major Customer [Line Items]        
Number of tenants 455   455 454
Revenues        
Revenue, Major Customer [Line Items]        
Number of tenants | Customer 0   0 0
Revenues | Minimum        
Revenue, Major Customer [Line Items]        
Rental revenue in percentage of total revenue     5.00% 5.00%
Shopko | Revenues        
Revenue, Major Customer [Line Items]        
Rental revenue in percentage of total revenue 10.40% 13.80%    
Shopko | Total assets | Customer Concentration Risk        
Revenue, Major Customer [Line Items]        
Rental revenue in percentage of total revenue     8.10% 10.70%
Shopko | Real estate investment portfolio | Customer Concentration Risk        
Revenue, Major Customer [Line Items]        
Rental revenue in percentage of total revenue     10.40% 13.10%