CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME
Rental income	$ 57,678	$ 49,997
Expenses:
Real estate taxes	6,503	5,479
Utility expenses	3,987	3,731
Other operating expenses	9,578	8,767
Depreciation and amortization	13,696	11,910
Acquisition related costs	34	49
General and administrative	3,249	3,002
Total expenses	37,047	32,938
Operating income	20,631	17,059
Interest and other income	11	8
Interest expense (including net amortization of debt premiums and deferred financing fees of $331 and $324, respectively)	(4,147)	(4,023)
Equity in earnings of an investee	76	45
Income before income tax expense	16,571	13,089
Income tax expense	(43)	(45)
Income from continuing operations	16,528	13,044
Discontinued operations:
Income from discontinued operations	30	15
Net gain on sale of properties from discontinued operations	8,168
Net income	24,726	13,059
Other comprehensive income:
Equity in unrealized loss of an investee	(8)	(1)
Other comprehensive income	(8)	(1)
Comprehensive income	$ 24,718	$ 13,058
Weighted average common shares outstanding (in shares)	54,645	47,052
Income from continuing operations per common share (in dollars per share)	$ 0.30	$ 0.28
Income from discontinued operations per common share (in dollars per share)	$ 0.15
Net income per common share (in dollars per share)	$ 0.45	$ 0.28