Investments in Real Estate (Details) ft² in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) ft² item	Dec. 31, 2015 USD ($) ft² item	Dec. 31, 2014 USD ($)
Real estate properties
Leasable square feet | ft²	83.0
Number of investments in properties that caused any tenant to be 10% of more of total assets | item	0
Total revenue	$ 1,103,172,000	$ 1,023,285,000	$ 933,505,000
Net income	316,477,000	284,855,000	269,140,000
Total capitalized costs on existing properties	35,535,952
In-place lease, depreciation and amortization to expense	94,000,000	87,900,000	83,600,000
Net Decrease to Rental Income for Capitalized above Market and below Market Leases	9,300,000	7,900,000	$ 8,000,000
Net increase (decrease) to rental revenue
2017	(10,076,000)
2018	(9,834,000)
2019	(8,880,000)
2020	(8,119,000)
2021	(6,842,000)
Thereafter	31,672,000
Totals	(12,079,000)
Increase to amortization expense
2017	97,299,000
2018	94,801,000
2019	84,477,000
2020	78,972,000
2021	70,783,000
Thereafter	379,703,000
Totals	$ 806,035,000
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	$ 1,860,000,000	$ 1,260,000,000
Number of properties | item	505	286
Initial weighted average contractual lease rate of properties acquired (as a percent)	6.30%	6.60%
Number of states in which properties are located | item	40	40
Leasable square feet | ft²	8.2	6.2
Leased area (as a percent)	100.00%	100.00%
Weighted average lease term	14 years 8 months 12 days	16 years 6 months
Number of industries in which tenants operate | item	28	21
Acquisition transaction costs	$ 346,000	$ 913,000
New properties and properties under development | Retail properties
Real estate properties
Property type- percentage of properties acquired	86.40%	87.30%
New properties and properties under development | Industrial and distribution properties
Real estate properties
Property type- percentage of properties acquired	13.60%	12.70%
Properties under development or expansion
Real estate properties
Number of properties | item	33	35
Initial weighted average contractual lease rate of properties acquired (as a percent)	7.10%	9.70%
Investments in properties	$ 103,800,000	$ 45,800,000
Aggregate acquisitions
Real estate properties
Land recorded related to acquisition	515,500,000	257,100,000
Buildings and improvements recorded	1,210,000,000	937,100,000
Intangible assets related to leases recorded	168,000,000	105,800,000
Intangible liabilities related to leases and other assumed liabilities recorded	30,600,000	40,900,000
Contingent consideration associated with acquisition	0	0
Total revenue	44,600,000	43,400,000
Net income	22,000,000	21,100,000
Amount of investment allocated by estimate	761,800,000
Amount of investment previously allocated by estimate finalized during the period	195,400,000
Investments in Existing Properties
Real estate properties
Total capitalized costs on existing properties	16,300,000	11,500,000
Re-leasing costs and real estate improvements included in capitalized costs on existing properties	797,000	748,000
Recurring Capital Expenditures Real Estate Improvements	679,000	7,600,000
Nonrecurring Building Real Estate Improvements	14,900,000	3,200,000
Real estate investments with existing leases
Real estate properties
Real estate acquired	$ 741,200,000	$ 391,400,000
Number of properties | item	90	86