Basis of Presentation - Variable Interest Entity Disclosure (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets
Land, buildings and improvements	$ 5,651,906	$ 5,457,265
Net investments in direct financing leases	705,588	721,607
In-place lease and other intangible assets	1,228,241	1,213,976
Above-market rent intangible assets	631,977	640,480
Accumulated depreciation and amortization	(1,445,397)	(1,329,613)
Total assets	8,266,700	8,231,402
Liabilities
Non-recourse mortgages, net	985,666	1,185,477
Total liabilities	4,953,731	4,819,052
Variable Interest Entity
Assets
Land, buildings and improvements	893,325	916,001
Net investments in direct financing leases	39,167	40,133
In-place lease and other intangible assets	269,371	268,863
Above-market rent intangible assets	101,919	103,081
Accumulated depreciation and amortization	(265,247)	(251,979)
Total assets	1,077,356	1,118,727
Liabilities
Non-recourse mortgages, net	115,209	128,230
Total liabilities	$ 186,648	$ 201,186