Investments in Real Estate - Properties with Existing Leases (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) property	Sep. 30, 2017 USD ($) property
Net decrease to rental revenue
2018	$ (4,388)
2019	(17,043)
2020	(16,314)
2021	(15,075)
2022	(13,369)
Thereafter	(46,164)
Totals	(112,352)
Increase to amortization expense
2018	26,568
2019	98,078
2020	92,326
2021	84,355
2022	72,765
Thereafter	416,571
Totals	790,662
In-Place Leases
Investments in real estate properties
Depreciation and amortization expense	79,800	$ 79,100
Rental Revenue
Investments in real estate properties
Amortization of above and below Market Leases	12,400	10,200
Real Estate Investment | New and under development or expansion
Investments in real estate properties
Value of properties acquired during the period	$ 1,470,000	$ 956,900
Number of properties acquired during the period | property	591	177
Initial weighted average contractual lease rate of properties acquired (as a percent)	6.30%	6.50%
Real Estate Investment | New and under development or expansion | In-Place Leases
Investments in real estate properties
Value of properties acquired during the period	$ 307,500	$ 562,100
Number of properties acquired during the period | property	147	68
Real Estate Investment | Properties under development
Investments in real estate properties
Value of properties acquired during the period	$ 69,700	$ 16,400
Number of properties acquired during the period | property	11	13
Initial weighted average contractual lease rate of properties acquired (as a percent)	6.80%	7.30%