Real Estate and Accumulated Depreciation (Notes to Schedule III) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate
Balance at beginning of period	$ 3,814,986	$ 2,606,343	$ 2,619,488
Additions during the period:
Acquisitions	62,723	0	28,131
Improvements and other capitalized costs	303,940	208,016	139,676
Transfers	0	5,306	0
Real estate additions, total	366,663	3,046,052	167,807
Deductions during the period:
Parkway spin-off	0	(1,230,235)	0
Cost of real estate sold	(287,850)	(602,648)	(180,952)
Impairment loss	0	(4,526)	0
Real estate deductions, total	(287,850)	(1,837,409)	(180,952)
Balance at end of period	3,893,799	3,814,986	2,606,343
Accumulated Depreciation
Balance at beginning of period	215,856	359,422	324,543
Additions during the period:
Acquisitions	0	0	0
Improvements and other capitalized costs	0	0	0
Transfers	0	0	0
Depreciation expense	101,720	112,277	99,067
Real estate accumulated depreciation additions, total	101,720	112,277	99,067
Deductions during the period:
Parkway spin-off	0	(148,523)	0
Cost of real estate sold	(41,599)	(107,320)	(64,188)
Impairment loss	0	0	0
Real estate accumulated depreciation deductions, total	(41,599)	(255,843)	(64,188)
Balance at end of period	275,977	215,856	359,422
Aggregate cost for federal income tax, net of depreciation	$ 2,900,000
Buildings and Improvements | Minimum
Deductions during the period:
Useful life	25 years
Buildings and Improvements | Maximum
Deductions during the period:
Useful life	42 years
Parkway merger
Additions during the period:
Acquisitions	$ 0	2,832,730	0
Additions during the period:
Acquisitions	$ 0	$ 0	$ 0