Schedule III - Real Estate and Accumulated Depreciation and Amortization - Notes to Schedule III (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Land, buildings, and leasehold interests:
Balance at the beginning of year	$ 8,448,702	$ 7,883,633	$ 7,314,132
Acquisitions, completed construction and tenant improvements	177,901	733,376	706,903
Disposition of land, buildings, and leasehold interests	(54,886)	(138,332)	(109,590)
Provision for loss on impairment of real estate	(37,442)	(29,975)	(27,812)
Balance at the close of year	8,534,275	8,448,702	7,883,633
Accumulated depreciation and amortization:
Balance at the beginning of year	1,151,667	1,016,271	881,121
Disposition of land, buildings, and leasehold interests	(17,828)	(44,185)	(28,076)
Depreciation and amortization expense	186,104	179,581	163,226
Balance at the close of year	1,319,943	1,151,667	1,016,271
Work in progress – improvements	26,673	27,438	$ 8,017
Mortgages payable, including unamortized premium and net of unamortized debt costs	11,395	$ 12,059
Mortgage Agreement
Accumulated depreciation and amortization:
Mortgages payable, including unamortized premium and net of unamortized debt costs	15,151
Operating Lease
Land, buildings, and leasehold interests:
Balance at the close of year	8,499,395
Accumulated depreciation and amortization:
Balance at the close of year	1,317,407
Real estate, federal income tax basis	8,451,933
Direct Financing Lease
Land, buildings, and leasehold interests:
Balance at the close of year	0
Accumulated depreciation and amortization:
Balance at the close of year	0
Real estate, federal income tax basis	$ 2,703