Consolidated Statements of Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Shares of Beneficial Interest at Par Value [Member]	Additional Paid in Capital [Member]	Distributions in Excess of Net Income Attributable to the Controlling Interests [Member]	Total Shareholders' Equity [Member]	Noncontrolling Interests in Subsidiaries [Member]
Balance at Dec. 31, 2012	$ 796,143	$ 664	$ 1,145,515	$ (354,122)	$ 792,057	$ 4,086
Balance (in shares) at Dec. 31, 2012		66,437
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to the controlling interests	12,598			12,598	12,598
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	390					390
Dividends	(40,099)			(40,099)	(40,099)
Share grants, net of share grant amortization and forfeitures	2,196	1	2,195		2,196
Share grants, net of share grant amortization and forfeitures (in shares)		63
Balance at Jun. 30, 2013	$ 771,228	$ 665	$ 1,147,710	$ (381,623)	$ 766,752	$ 4,476
Balance (in shares) at Jun. 30, 2013		66,500