Schedule III - Real Estate and Accumulated Depreciation and Amortization - Notes to Schedule III (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Land, buildings, and leasehold interests:
Balance at the beginning of year	$ 7,314,132	$ 6,647,597	$ 5,913,547
Acquisitions, completed construction and tenant improvements	706,903	744,577	833,764
Disposition of land, buildings, and leasehold interests	(109,590)	(73,089)	(91,818)
Provision for loss on impairment of real estate	(27,812)	(4,953)	(7,896)
Balance at the close of year	7,883,633	7,314,132	6,647,597
Accumulated depreciation and amortization:
Balance at the beginning of year	881,121	742,467	624,607
Disposition of land, buildings, and leasehold interests	(28,076)	(14,035)	(16,286)
Depreciation and amortization expense	163,226	152,689	134,146
Balance at the close of year	1,016,271	881,121	742,467
Work in progress - improvements	8,017	41,920	$ 24,057
Mortgages payable, including unamortized premium and net of unamortized debt costs	12,694	$ 13,300
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	7,855,114
Accumulated depreciation and amortization:
Balance at the close of year	1,009,374
Real estate, federal income tax basis	7,764,828
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