Consolidated Statement Of Changes In Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Preferred Stock [Member]	Additional paid-in capital [Member]	Treasury shares [Member]	Accumulated other comprehensive income (loss) [Member]	Distributions in excess of net income [Member]	Noncontrolling Interests [Member]
Balance at Dec. 31, 2011	$ 1,498,103
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of nonvested shares, including nonvested shares issued for the payment of bonuses (in shares)		148,095	0
Issuance of nonvested shares, including nonvested shares issued for the payment of bonuses	1,487	1	0	1,486	0	0	0	0
Cancellation of 185 employee nonvested shares	0			5	(5)
Amortization of nonvested shares	2,266			2,266	0	0	0	0
Share option expense	481			481	0	0	0	0
Foreign currency translation adjustment	(124)			0	0	(124)	0	0
Change in unrealized gain/loss on derivatives	(2,659)			0	0	(2,659)	0	0
Net income	58,208			0	0	0	58,171	37
Purchase of 73,411 common shares for treasury	(3,209)			0	(3,209)	0	0	0
Issuances of common shares (in shares)		4,464	0
Issuances of common shares	197	0	0	197	0	0	0	0
Stock option exercises, net (in shares)	53,430	53,430	0
Stock option exercises, net	(480)	(1)	0	(1,010)	(1,491)	0	0	0
Dividends to common and preferred shareholders	(82,248)			0	0	0	(82,248)	0
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	27,785
Balance at Jun. 30, 2012	$ 1,472,510	$ 482	$ 135	$ 1,752,784	$ (49,539)	$ 20,680	$ (252,338)	$ 306
Balance (in shares) at Jun. 30, 2012		48,279,507	13,450,000