Summary of Significant Accounting Policies - Variable Interest Entity Disclosure (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Real estate — Land, buildings and improvements	$ 2,772,611	$ 2,745,424
Operating real estate — Land, buildings and improvements	340,772	258,971
Net investments in direct financing leases	509,228	508,392
In-place lease intangible assets	629,961	620,149
Accumulated depreciation and amortization	(626,655)	(506,238)
Other assets, net	322,201	228,717
Total assets	4,587,470	4,698,923
Liabilities
Mortgage debt, net	1,849,459	2,022,250
Accounts payable, accrued expenses and other liabilities	132,751	128,911
Deferred income taxes	30,524	32,655
Total liabilities	2,244,213	2,383,919
Variable Interest Entity, Primary Beneficiary
Assets
Real estate — Land, buildings and improvements	109,426	225,347
Operating real estate — Land, buildings and improvements	80,658	11,388
Net investments in direct financing leases	312,234	315,251
In-place lease intangible assets	8,650	8,795
Accumulated depreciation and amortization	(26,395)	(25,000)
Other assets, net	73,620	52,565
Total assets	567,929	590,526
Liabilities
Mortgage debt, net	104,213	192,839
Accounts payable, accrued expenses and other liabilities	12,693	11,187
Deferred income taxes	12,374	15,687
Total liabilities	$ 129,662	220,077
Variable Interest Entity, Primary Beneficiary | Adjustments
Assets
Real estate — Land, buildings and improvements		(111,100)
In-place lease intangible assets		(21,800)
Accumulated depreciation and amortization		21,600
Other assets, net		(13,000)
Total assets		(124,400)
Liabilities
Mortgage debt, net		(73,000)
Accounts payable, accrued expenses and other liabilities		(3,300)
Total liabilities		$ (76,600)