Consolidated Statement Of Shareholders' Equity (USD $) In Thousands, except Share data	Total	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Dividends in Excess of Net Income [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]
Beginning balance at Dec. 31, 2013	$ 1,471,297	$ 9,997	$ 667	$ 2,062,708	$ (623,795)	$ (1,417)	$ 23,137
Beginning balance (in shares) at Dec. 31, 2013		399,896	66,701,422
Net income, excluding $764 attributable to redeemable noncontrolling interests	39,781				38,753		1,028
Other comprehensive loss - change in value of interest rate swaps	(543)					(543)
Dividends declared to common shareholders	(52,461)				(52,461)
Dividends declared to preferred shareholders	(135)				(135)
Distributions declared to noncontrolling interests	(985)						(985)
Common shares issued (in shares)			455,735
Common shares issued	50,158		5	50,153
Exercise of stock options (in shares)			18,610
Exercise of stock options	1,392		0	1,392
Shares issued under dividend reinvestment plan (in shares)			4,908
Shares issued under dividend reinvestment plan	515			515
Share-based compensation expense, net of shares withheld for employee taxes (in shares)			86,355
Share-based compensation expense, net of shares withheld for employee taxes	222		1	221
Contribution from noncontrolling interests	65,350						65,350
Adjustment to redeemable noncontrolling interests	(323)			(323)			0
Ending balance at Mar. 31, 2014	$ 1,574,268	$ 9,997	$ 673	$ 2,114,666	$ (637,638)	$ (1,960)	$ 88,530
Ending balance (in shares) at Mar. 31, 2014		399,896	67,267,030