Schedule III - Real Estate and Accumulated Depreciation and Amortization - Notes to Schedule III (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Land, buildings, and leasehold interests:
Balance at the beginning of year	$ 7,883,633	$ 7,314,132	$ 6,647,597
Acquisitions, completed construction and tenant improvements	733,376	706,903	744,577
Disposition of land, buildings, and leasehold interests	(138,332)	(109,590)	(73,089)
Provision for loss on impairment of real estate	(29,975)	(27,812)	(4,953)
Balance at the close of year	8,448,702	7,883,633	7,314,132
Accumulated depreciation and amortization:
Balance at the beginning of year	1,016,271	881,121	742,467
Disposition of land, buildings, and leasehold interests	(44,185)	(28,076)	(14,035)
Depreciation and amortization expense	179,581	163,226	152,689
Balance at the close of year	1,151,667	1,016,271	881,121
Work in progress - improvements	27,438	8,017	$ 41,920
Mortgages payable, including unamortized premium and net of unamortized debt costs	12,059	$ 12,694
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	8,410,864
Accumulated depreciation and amortization:
Balance at the close of year	1,148,277
Real estate, federal income tax basis	8,338,530
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