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 $1,640 attributable to redeemable noncontrolling interests	84,321				82,298		2,023
Other comprehensive loss - change in value of interest rate swaps	(2,643)					(2,643)
Dividends declared to common shareholders	(105,238)				(105,238)
Dividends declared to preferred shareholders	(271)				(271)
Distributions declared to noncontrolling interests	(2,201)						(2,201)
Common shares issued (in shares)			896,545
Common shares issued	102,339		9	102,330
Exercise of stock options (in shares)			19,610
Exercise of stock options	1,461		1	1,460
Shares issued under dividend reinvestment plan (in shares)			9,443
Shares issued under dividend reinvestment plan	1,031			1,031
Share-based compensation expense, net of shares withheld for employee taxes (in shares)			85,346
Share-based compensation expense, net of shares withheld for employee taxes	3,292		1	3,291
Redemption of Operating Partnership Units (in shares)			0
Redemption Of Operating Partnership Units	(53)			(39)			(14)
Contributions from noncontrolling interests	65,350						65,350
Adjustment to redeemable noncontrolling interests	(629)			(629)			0
Ending balance at Jun. 30, 2014	$ 1,618,056	$ 9,997	$ 678	$ 2,170,152	$ (647,006)	$ (4,060)	$ 88,295
Ending balance (in shares) at Jun. 30, 2014		399,896	67,712,366