Condensed Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Treasury Stock	Distributions in Excess of Net Income	Stockholders’ Investment	Nonredeemable Noncontrolling Interests
Beginning balance at Dec. 31, 2016	$ 2,514,240	$ 6,867	$ 403,747	$ 3,407,430	$ (148,373)	$ (1,214,114)	$ 2,455,557	$ 58,683
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	175,803					172,840	172,840	2,963
Common stock issued pursuant to:
Common stock offering, net of issuance costs	211,820		25,000	186,820			211,820
Stock-based compensation	299		353	(54)			299
Spin-off of Parkway, Inc.	562					562	562
Common stock redemption by unit holders	0		1,203	8,865			10,068	(10,068)
Amortization of stock options and restricted stock, net of forfeitures	969		(6)	975			969
Contributions from nonredeemable noncontrolling interests	900							900
Distributions to nonredeemable noncontrolling interest	(966)							(966)
Common dividends	(73,950)					(73,950)	(73,950)
Ending balance at Jun. 30, 2017	2,829,677	6,867	430,297	3,604,036	(148,373)	(1,114,662)	2,778,165	51,512
Common stock issued pursuant to:
Cumulative effect of change in accounting principle	22,329					22,329	22,329
Beginning balance at Dec. 31, 2017	2,825,111	6,867	430,350	3,604,776	(148,373)	(1,121,647)	2,771,973	53,138
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,155					37,319	37,319	836
Common stock issued pursuant to:
Stock-based compensation	(567)		397	(864)	(100)		(567)
Amortization of stock options and restricted stock, net of forfeitures	1,122		(13)	1,135			1,122
Contributions from nonredeemable noncontrolling interests	1,708							1,708
Distributions to nonredeemable noncontrolling interest	(873)							(873)
Common dividends	(54,641)					(54,641)	(54,641)
Ending balance at Jun. 30, 2018	$ 2,832,344	$ 6,867	$ 430,734	$ 3,605,047	$ (148,473)	$ (1,116,640)	$ 2,777,535	$ 54,809