Consolidated Statement Of Shareholders' Equity - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Total	Preferred Shares	Common Shares	Additional Paid-in Capital	Accumulated Dividends in Excess of Net Income	Accumulated Other Comprehensive Income	Noncontrolling Interests	Common Shares Additional Paid-in Capital
Beginning balance (in shares) at Dec. 31, 2017		405,896	73,090,877
Beginning balance at Dec. 31, 2017	$ 2,391,514	$ 159,997	$ 733	$ 2,855,321	$ (749,367)	$ 22	$ 124,808
Increase (Decrease) in Stockholders' Equity [Roll Forward]
January 1, 2018 adoption of new accounting standard - See Note 2	(6,028)				(6,028)
Net income, excluding $1,015 attributable to redeemable noncontrolling interests	61,916				61,247		669
Other comprehensive income - change in fair value of interest rate swaps	467					467
Dividends declared to common shareholders	(73,153)				(73,153)
Dividends declared to preferred shareholders	(2,010)				(2,010)
Distributions declared to noncontrolling interests	(1,348)						(1,348)
Shares issued (in shares)			30
Shares issued	4							$ 4
Exercise of stock options (in shares)			30,000
Exercise of stock options	1,262		$ 1	1,261
Shares issued under dividend reinvestment plan (in shares)			4,440
Shares issued under dividend reinvestment plan	547			547
Share-based compensation expense, net of forfeitures (in shares)			97,968
Share-based compensation expense, net of forfeitures	3,870		$ 1	3,869
Shares withheld for employee taxes (in shares)			(6,795)
Shares withheld for employee taxes	(753)			(753)
Redemption of OP units	(3,178)			(532)			(2,646)
Ending balance (in shares) at Mar. 31, 2018		405,896	73,216,520
Ending balance at Mar. 31, 2018	$ 2,373,110	$ 159,997	$ 735	$ 2,859,717	$ (769,311)	$ 489	$ 121,483