Investments in Real Estate - Acquisitions (Details) ft² in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) ft² state property_investment industry property	Mar. 31, 2018 USD ($) ft² state industry property
Investments in real estate properties
Leasable square feet (sq ft) | ft²	95,200
Revenues	$ 354,365,000	$ 318,295,000
Net income (loss)	$ 111,230,000	83,315,000
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	$ 3,500,000	296,000
Net income (loss)	1,800,000	(215,000)
Real Estate Investment | New and under development or expansion
Investments in real estate properties
Value of properties acquired during the period	$ 519,500,000	$ 509,800,000
Number of properties acquired during the period | property	105	174
Initial weighted average contractual lease rate of properties acquired (as a percent)	6.70%	6.20%
Number of states in which properties are located | state	25	27
Leasable square feet (sq ft) | ft²	2,300	954
Leased area (as a percent)	100.00%	100.00%
Weighted average lease term	16 years 11 months 23 days	14 years
Property investments allocated to land	$ 119,200,000	$ 209,600,000
Property investments allocated to buildings and improvements	345,300,000	255,400,000
Property investments allocated to lease-related intangible assets	37,400,000	57,600,000
Property investments allocated to loan receivables	22,600,000
Property investments allocated to lease-related intangible liabilities and other assumed liabilities	5,000,000	12,800,000
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	14	12
Real Estate Investment | New properties | Retail
Investments in real estate properties
Property type acquired (as a percent)	98.70%	100.00%
Real Estate Investment | New properties | Industrial
Investments in real estate properties
Property type acquired (as a percent)	1.30%
Real Estate Investment | Properties under development
Investments in real estate properties
Value of properties acquired during the period	$ 10,900,000	$ 3,800,000
Number of properties acquired during the period | property	8	6
Initial weighted average contractual lease rate of properties acquired (as a percent)	7.20%	6.70%
Real Estate Investment | Maximum
Investments in real estate properties
Investments to any one tenant as a percentage of total assets	10.00%