Real Estate and Accumulated Depreciation (Notes to Schedule III) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real Estate
Balance at beginning of period	$ 2,606,343	$ 2,619,488	$ 2,164,815
Additions during the period:
Acquisitions	0	28,131	523,695
Improvements and other capitalized costs	208,016	139,676	109,959
Transfers	5,306	0	0
Real estate additions, total	3,046,052	167,807	633,654
Deductions during the period:
Parkway spin-off	(1,230,235)	0	0
Cost of real estate sold	(602,648)	(180,952)	(178,981)
Impairment loss	(4,526)	0	0
Real estate deductions, total	(1,837,409)	(180,952)	(178,981)
Balance at end of period	3,814,986	2,606,343	2,619,488
Accumulated Depreciation
Balance at beginning of period	359,422	324,543	257,151
Additions during the period:
Acquisitions	0	0	0
Improvements and other capitalized costs	0	0	0
Transfers	0	0	0
Depreciation expense	112,277	99,067	86,824
Real estate accumulated depreciation additions, total	112,277	99,067	86,824
Deductions during the period:
Parkway spin-off	(148,523)	0	0
Cost of real estate sold	(107,320)	(64,188)	(19,432)
Impairment loss	0	0	0
Real estate accumulated depreciation deductions, total	(255,843)	(64,188)	(19,432)
Balance at end of period	215,856	359,422	324,543
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
Additions during the period:
Acquisitions	$ 2,832,730	0	0
Additions during the period:
Acquisitions	$ 0	$ 0	$ 0