CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME
Rental income	$ 226,910	$ 203,700	$ 168,074
Expenses:
Real estate taxes	25,710	22,485	18,426
Utility expenses	17,116	15,767	13,918
Other operating expenses	41,134	37,074	29,773
Depreciation and amortization	55,699	49,070	37,776
Acquisition related costs	2,439	1,614	3,504
General and administrative	12,710	11,924	10,469
Total expenses	154,808	137,934	113,866
Operating income	72,102	65,766	54,208
Interest and other income	37	29	104
Interest expense (including net amortization of debt premiums and deferred financing fees of $1,340, $1,332 and $1,045, respectively)	(16,831)	(16,892)	(12,057)
Income from continuing operations before income tax expense and equity in earnings of an investee	55,308	48,903	42,255
Income tax expense	(133)	(159)	(203)
Equity in earnings of an investee	334	316	139
Income from continuing operations	55,509	49,060	42,191
Income (loss) from discontinued operations	(889)	900	3,806
Net income	54,620	49,960	45,997
Other Comprehensive income (loss):
Equity in unrealized gain (loss) of an investee	(50)	22	75
Other Comprehensive income (loss)	(50)	22	75
Comprehensive income	$ 54,570	$ 49,982	$ 46,072
Weighted average common shares outstanding (in shares)	54,680	48,617	43,368
Per common share amounts:
Income from continuing operations per common share (in dollars per share)	$ 1.02	$ 1.01	$ 0.97
Income (loss) from discontinued operations per common share (in dollars per share)	$ (0.02)	$ 0.02	$ 0.09
Net income per common share (in dollars per share)	$ 1.00	$ 1.03	$ 1.06