Consolidated Statement Of Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Shares	Common shares	Additional Paid-in Capital	Accumulated Dividends in Excess of Net Income	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Beginning balance (in shares) at Dec. 31, 2012		399,896	64,815,446
Beginning balance at Dec. 31, 2012	$ 1,310,593	$ 9,997	$ 648	$ 1,875,525	$ (586,970)	$ (12,388)	$ 23,781
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income, excluding amount attributable to noncontrolling interests	164,721				162,681		2,040
Other comprehensive (loss) income - change in value of interest rate swaps	10,971					10,971
Dividends declared to common shareholders	(198,965)				(198,965)
Dividends declared to preferred shareholders	(541)				(541)
Distributions declared to noncontrolling interests	(1,887)						(1,887)
Common shares issued (in shares)			1,735,089
Common shares issued	185,182		$ 18	185,164
Exercise of stock options (in shares)			16,554
Exercise of stock options	$ 1,015		$ 0	1,015
Shares issued under dividend reinvestment plan (in shares)	20,026		20,026
Shares issued under dividend reinvestment plan	$ 2,130			2,130
Share-based compensation expense, net of forfeitures (in shares)			108,803
Share-based compensation expense, net of forfeitures	11,199		$ 1	11,198
Common Shares withheld for employee taxes (in shares)			(16,972)
Shares withheld for employee taxes (net value)				(1,842)
Conversion and redemption of OP units (in shares)			22,476
Conversion and redemption of OP units	1,422			625			797
Adjustment to redeemable noncontrolling interests	(9,857)			(9,857)
Ending balance (in shares) at Dec. 31, 2013		399,896	66,701,422
Ending balance at Dec. 31, 2013	1,471,297	$ 9,997	$ 667	2,062,708	(623,795)	(1,417)	23,137
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income, excluding amount attributable to noncontrolling interests	168,837				164,535		4,302
Other comprehensive (loss) income - change in value of interest rate swaps	(2,098)
Dividends declared to common shareholders	(224,190)				(224,190)
Dividends declared to preferred shareholders	(541)				(541)
Distributions declared to noncontrolling interests	(4,620)						(4,620)
Common shares issued (in shares)			1,768,703
Common shares issued	213,580		$ 18	213,562
Exercise of stock options (in shares)			29,218
Exercise of stock options	$ 2,262		$ 1	2,261
Shares issued under dividend reinvestment plan (in shares)	18,705		18,705
Shares issued under dividend reinvestment plan	$ 2,168			2,168
Share-based compensation expense, net of forfeitures (in shares)			117,647
Share-based compensation expense, net of forfeitures	12,941		$ 1	12,940
Common Shares withheld for employee taxes (in shares)			(29,912)
Shares withheld for employee taxes (net value)				(3,335)
Conversion and redemption of OP units (in shares)			0
Conversion and redemption of OP units	63			49			14
Contributions from noncontrolling interests	65,350						65,350
Adjustment to redeemable noncontrolling interests	(9,032)			(9,032)
Ending balance (in shares) at Dec. 31, 2014		399,896	68,605,783
Ending balance at Dec. 31, 2014	1,692,556	$ 9,997	$ 687	2,281,223	(683,991)	(3,515)	88,155
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income, excluding amount attributable to noncontrolling interests	215,001				210,219		4,782
Other comprehensive (loss) income - change in value of interest rate swaps	(595)
Dividends declared to common shareholders	(250,388)				(250,388)
Dividends declared to preferred shareholders	(541)				(541)
Distributions declared to noncontrolling interests	(5,269)						(5,269)
Common shares issued (in shares)			813,548
Common shares issued	$ 108,545		$ 8	108,537
Exercise of stock options (in shares)	29,940		29,940
Exercise of stock options	$ 1,991		$ 0	1,991
Shares issued under dividend reinvestment plan (in shares)	16,524		16,524
Shares issued under dividend reinvestment plan	$ 2,296			2,296
Share-based compensation expense, net of forfeitures (in shares)			52,213
Share-based compensation expense, net of forfeitures	12,074		$ 1	12,073
Common Shares withheld for employee taxes (in shares)			(64,227)
Shares withheld for employee taxes (net value)				(9,211)
Conversion and redemption of OP units (in shares)			39,611
Conversion and redemption of OP units	151			4,072			4,223
Contributions from noncontrolling interests	34,737						34,737
Adjustment to redeemable noncontrolling interests	(19,114)			(19,114)
Ending balance (in shares) at Dec. 31, 2015		399,896	69,493,392
Ending balance at Dec. 31, 2015	$ 1,781,931	$ 9,997	$ 696	$ 2,381,867	$ (724,701)	$ (4,110)	$ 118,182