Basis of Presentation - Variable Interest Entity Disclosure (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Land, buildings and improvements	$ 5,523,209	$ 5,457,265
Net investments in direct financing leases	725,676	721,607
In-place lease and other intangible assets	1,235,828	1,213,976
Above-market rent intangible assets	639,057	640,480
Accumulated depreciation and amortization	(1,399,810)	(1,329,613)
Total assets	8,287,871	8,231,402
Liabilities
Non-recourse mortgages, net	1,005,868	1,185,477
Total liabilities	4,917,401	4,819,052
Variable Interest Entity
Assets
Land, buildings and improvements	945,949	916,001
Net investments in direct financing leases	40,644	40,133
In-place lease and other intangible assets	286,512	268,863
Above-market rent intangible assets	104,219	103,081
Accumulated depreciation and amortization	(257,816)	(251,979)
Total assets	1,199,580	1,118,727
Liabilities
Non-recourse mortgages, net	118,328	128,230
Total liabilities	$ 194,988	$ 201,186