CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues:
Rental income	$ 591,933	$ 515,780	$ 457,819
Property other income	52,105	45,621	40,864
Other income	310	155	106
Total revenues	644,348	561,556	498,789
Expenses:
Operating and maintenance	235,040	217,069	203,421
General and administrative	34,174	29,145	25,138
Interest	125,809	127,618	120,652
Depreciation and amortization	165,642	140,713	122,772
Other expenses	2,741	3,225	2,871
Total expenses	563,406	517,770	474,854
Income from continuing operations	80,942	43,786	23,935
Discontinued operations:
Income from discontinued operations	2,148	3,878	2,396
Gain (loss) on disposition of property	80,532		(13)
Discontinued operations	82,680	3,878	2,383
Net income	163,622	47,664	26,318
Net income attributable to noncontrolling interest	(28,320)	(9,808)	(6,237)
Net income attributable to common stockholders	$ 135,302	$ 37,856	$ 20,081
Basic earnings per share data:
Income from continuing operations (in dollars per share)	$ 1.34	$ 0.83	$ 0.50
Discontinued operations (in dollars per share)	$ 1.38	$ 0.07	$ 0.05
Net income attributable to common stockholders (in dollars per share)	$ 2.72	$ 0.90	$ 0.55
Diluted earnings per share data:
Income from continuing operations (in dollars per share)	$ 1.33	$ 0.82	$ 0.49
Discontinued operations (in dollars per share)	$ 1.36	$ 0.07	$ 0.05
Net income attributable to common stockholders (in dollars per share)	$ 2.69	$ 0.89	$ 0.54
Weighted average number of shares outstanding:
Basic (in shares)	49,744,636	41,860,139	36,682,191
Diluted (in shares)	50,382,636	42,545,082	37,169,886