Schedule III - Real Estate and Accumulated Depreciation and Amortization Notes to Schedule III (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance at the beginning of year	$ 5,236,251	$ 4,686,844	$ 4,145,368
Acquisitions, completed construction and tenant improvements	717,899	601,168	602,836
Disposition of land, buildings, and leasehold interests	(36,633)	(50,938)	(57,254)
Provision for loss on impairment of real estate	(3,970)	(823)	(4,106)
Balance at the close of year	5,913,547	5,236,251	4,686,844
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance at the beginning of year	513,175	418,136	333,778
Disposition of land, buildings, and leasehold interests	(7,377)	(9,153)	(6,778)
Depreciation and amortization expense	118,809	104,192	91,136
Balance at the close of year	624,607	513,175	418,136
Work in progress	61,354	28,908	$ 60,720
Mortgages payable, including unamortized premium and net of unamortized debt costs	23,964	$ 26,182
Operating Lease
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance at the close of year	5,815,108
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance at the close of year	620,188
Real estate, federal income tax basis	5,801,797
Direct Financing Lease
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance at the close of year	0
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance at the close of year	0
Real estate, federal income tax basis	2,703
Mortgage Agreement-2
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Mortgages payable, including unamortized premium and net of unamortized debt costs	6,952
Mortgage Agreement-3
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Mortgages payable, including unamortized premium and net of unamortized debt costs	$ 15,151