Significant Credit and Revenue Concentration - Narrative (Details)
12 Months Ended 3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Revenue, Major Customer [Line Items]        
Number of tenants 454 377 454 377
Sales [Member] | Customer Concentration Risk [Member]        
Revenue, Major Customer [Line Items]        
Number of tenants 0 0 0 0
Shopko and Pamida [Member] | Customer Concentration Risk [Member]        
Revenue, Major Customer [Line Items]        
Rental revenue by combined properties operated by tenants 13.10% 14.40%    
Shopko and Pamida [Member] | Sales [Member] | Customer Concentration Risk [Member]        
Revenue, Major Customer [Line Items]        
Rental revenue in percentage of total revenue     14.00% 14.80%
Minimum [Member] | Sales [Member] | Customer Concentration Risk [Member]        
Revenue, Major Customer [Line Items]        
Rental revenue in percentage of total revenue 5.00% 10.00%