Schedule III - Real Estate and Accumulated Depreciation - Reconciliation of Gross Real Estate Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate [Roll Forward]
Balance, beginning of year	$ 13,577,700	$ 13,539,921	$ 14,566,343
Additions:
Acquisitions	437,227	634,080	91,052
Improvements	31,898	28,503	25,781
Deductions/Other:
Dispositions	(368,808)	(505,403)	(878,552)
Impairments	(84,278)	(82,292)	(228,750)
Reclassification to assets held for sale	(2,997)	(52,376)	(36,722)
Other	1,698	15,267	769
Balance, end of year	$ 13,592,440	$ 13,577,700	$ 13,539,921