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	188,088					184,907	184,907	3,181
Common stock issued pursuant to:
Common stock offering, net of issuance costs	211,774		25,000	186,774			211,774
Stock-based compensation	124		403	(279)			124
Spin-off of Parkway, Inc.	545					545	545
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	1,476		(3)	1,479			1,476
Contributions from nonredeemable noncontrolling interests	1,588							1,588
Distributions to nonredeemable noncontrolling interest	(1,364)							(1,364)
Common dividends	(99,151)					(99,151)	(99,151)
Ending balance at Sep. 30, 2017	2,817,320	6,867	430,350	3,604,269	(148,373)	(1,127,813)	2,765,300	52,020
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	58,014					56,804	56,804	1,210
Common stock issued pursuant to:
Stock-based compensation	(567)		397	(864)	(100)		(567)
Amortization of stock options and restricted stock, net of forfeitures	1,683		(22)	1,705			1,683
Contributions from nonredeemable noncontrolling interests	1,960							1,960
Distributions to nonredeemable noncontrolling interest	(2,071)							(2,071)
Common dividends	(82,004)					(82,004)	(82,004)
Ending balance at Sep. 30, 2018	$ 2,824,455	$ 6,867	$ 430,725	$ 3,605,617	$ (148,473)	$ (1,124,518)	$ 2,770,218	$ 54,237