Investments in Real Estate (Details) (USD $)
3 Months Ended
Mar. 31, 2015
item
sqft
Mar. 31, 2014
Real estate properties    
Leasable square feet 71,600,000  
Number of investments in properties that caused any tenant to be 10% of more of total assets 0  
Mortgages acquired   $ 45,900,000
Contingent consideration associated with acquisition 0 0
Total revenue 246,867,000 221,572,000
Income from continuing operations 67,581,000 54,916,000
In-place lease, depreciation and amortization to expense 21,600,000 20,100,000
Net (increase) decrease to rental income for capitalized above market and below market leases 1,700,000 2,000,000
Net increase (decrease) to rental revenue    
2015 (5,889,000)  
2016 (7,864,000)  
2017 (7,809,000)  
2018 (7,549,000)  
2019 (6,563,000)  
Thereafter 29,291,000  
Totals (6,383,000)  
Increase to amortization expense    
2015 65,083,000  
2016 86,533,000  
2017 85,333,000  
2018 82,889,000  
2019 72,831,000  
Thereafter 429,602,000  
Totals 822,271,000  
Maximum    
Real estate properties    
Investments to any one tenant as a percentage of total assets 10.00%  
New properties and properties under development    
Real estate properties    
Real estate acquired 209,900,000 656,700,000
Number of properties 83 337
Initial weighted average contractual lease rate of properties acquired (as a percent) 6.90% 7.00%
Number of states in which properties are located 24 35
Leasable square feet 1,600,000 4,500,000
Leased area (as a percent) 100.00% 100.00%
Weighted average lease term 15 years 6 months 14 years 2 months 12 days
Number of industries in which tenants operate 12 15
Acquisition transaction costs 94,000 454,000
New properties and properties under development | Retail properties    
Real estate properties    
Property type- percentage of properties acquired 74.20% 87.60%
New properties and properties under development | Office properties    
Real estate properties    
Property type- percentage of properties acquired   4.60%
New properties and properties under development | Industrial and distribution properties    
Real estate properties    
Property type- percentage of properties acquired 25.80% 7.80%
Properties under development or expansion    
Real estate properties    
Number of properties 25 13
Initial weighted average contractual lease rate of properties acquired (as a percent) 9.00% 8.40%
Investments in properties 15,300,000 13,400,000
Aggregate acquisitions    
Real estate properties    
Real estate acquired 209,900,000 656,700,000
Discounts/(Premiums) recorded upon assumption of mortgages   2,800,000
Land recorded related to acquisition 39,800,000 132,200,000
Buildings and improvements recorded 121,200,000 455,300,000
Intangible assets related to leases recorded 41,600,000 74,000,000
Other assets recorded 14,100,000 901,000
Intangible liabilities related to leases and other assumed liabilities recorded 6,800,000 8,500,000
Mortgages acquired   45,900,000
Total revenue 1,500,000 7,900,000
Income from continuing operations 712,000 3,200,000
Amount of investment allocated by estimate 197,700,000  
Amount of investment previously allocated by estimate finalized during the period 147,100,000  
Investments in Existing Properties    
Real estate properties    
Total capitalized costs on existing properties 1,300,000 1,400,000
Re-leasing costs included in capitalized costs on existing properties 313,000 192,000
Building and tenant improvements included in capitalized costs on existing properties 1,000,000 1,200,000
Real estate investments with existing leases    
Real estate properties    
Real estate acquired $ 114,200,000 $ 403,800,000
Number of properties 14 90