Consolidated Statements Of Operations (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues:
Rental income	$ 532,365	$ 473,833	$ 457,690
Property other income	47,454	42,640	40,727
Other income	154	106	759
Total revenues	579,973	516,579	499,176
Expenses:
Operating and maintenance	224,537	211,038	207,293
General and administrative	29,145	25,138	24,476
Interest	130,583	124,126	121,765
Depreciation and amortization	144,819	126,668	118,573
Other expenses	3,225	2,871
Total expenses	532,309	489,841	472,107
Income from continuing operations	47,664	26,738	27,069
Discontinued operations:
Income (loss) from discontinued operations		(407)	(4,305)
Gain (loss) on disposition of property		(13)	24,314
Discontinued operations		(420)	20,009
Net income	47,664	26,318	47,078
Net income attributable to noncontrolling interest	(9,808)	(6,237)	(12,659)
Net income attributable to common stockholders	$ 37,856	$ 20,081	$ 34,419
Basic earnings per share data:
Income from continuing operations	$ 0.90	$ 0.56	$ 0.60
Discontinued operations		$ (0.01)	$ 0.44
Net income attributable to common stockholders	$ 0.90	$ 0.55	$ 1.04
Diluted earnings per share data:
Income from continuing operations	$ 0.89	$ 0.55	$ 0.60
Discontinued operations		$ (0.01)	$ 0.44
Net income attributable to common stockholders	$ 0.89	$ 0.54	$ 1.04
Weighted average number of shares outstanding:
Basic	41,860,139	36,682,191	33,040,839
Diluted	42,545,082	37,169,886	33,172,116
Dividends declared per share	$ 2.48	$ 2.32	$ 2.68