Supplemental Cash Flow Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Disclosures:
Cash paid for interest	$ 260,951	$ 317,170	$ 343,854
Cash paid for income taxes	11,280	20,279	14,179
Cash received from federal income tax refund	16,686	0	0
Non-cash investing and financing activities:
Accrued capital expenditures and real estate developments	6,578	7,701	1,499
Accrued deferred financing costs	0	3	0
Distributions declared and unpaid	149,768	149,281	133,817
Accrued equity issuance costs	0	9	0
Mortgage note payable relieved by foreclosure or a deed-in-lieu of foreclosure	100,388	38,050	53,798
Mortgage notes payable assumed in real estate disposition	66,000	55,000	425,021
Real estate investments received from a ground lease expiration	259	0	0
Real estate investments received from a property-related legal settlement	775	0	0
Nonmonetary Exchanges:
Real estate investments received	50,204	0	0
Real estate investments relinquished and gain on disposition	(47,474)	0	0
Rent and tenant receivables, intangible lease liability and other assets, net	$ (2,511)	$ 0	$ 0