Investments in Real Estate - Acquisitions (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) ft² state property_investment industry property	Dec. 31, 2017 USD ($) ft² state industry property	Dec. 31, 2016 USD ($)
Investments in real estate properties
Leasable square feet | ft²	93,300,000
Net income	$ 364,598,000	$ 319,318,000	$ 316,477,000
Real Estate Investment
Investments in real estate properties
Number of investments in properties that caused any tenant to be 10% of more of total assets | property_investment	0
Revenues	$ 57,300,000	37,100,000
Net income	30,900,000	17,900,000
Real Estate Investment | New and under development or expansion
Investments in real estate properties
Value of properties acquired during the period	$ 1,800,000,000	$ 1,520,000,000
Number of properties acquired during the period | property	764	303
Initial weighted average contractual lease rate of properties acquired (as a percent)	6.40%	6.40%
Number of states in which properties are located | state	39	40
Leasable square feet | ft²	5,200,000	7,800,000
Leased area (as a percent)	100.00%	100.00%
Weighted average lease term	14 years 9 months 18 days	14 years 4 months 24 days
Property investments allocated to land	$ 657,900,000	$ 365,000,000
Property investments allocated to buildings and improvements	1,000,000,000	955,200,000
Property investments allocated to lease-related intangible assets	135,200,000	246,300,000
Property investments allocated to lease-related intangible liabilities and other assumed liabilities	35,800,000	47,000,000
Contingent consideration associated with acquisition	$ 0	$ 0
Real Estate Investment | New properties
Investments in real estate properties
Number of industries in which tenants operate | industry	21	23
Real Estate Investment | New properties | Retail
Investments in real estate properties
Property type acquired (as a percent)	96.30%	94.50%
Real Estate Investment | New properties | Industrial
Investments in real estate properties
Property type acquired (as a percent)	3.70%	5.50%
Real Estate Investment | Properties under development
Investments in real estate properties
Value of properties acquired during the period	$ 80,300,000	$ 21,200,000
Number of properties acquired during the period | property	14	17
Initial weighted average contractual lease rate of properties acquired (as a percent)	6.90%	6.90%
Real Estate Investment | Maximum
Investments in real estate properties
Investments to any one tenant as a percentage of total assets	10.00%