Condensed Consolidated Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenues:
Property rental	$ 107,340	$ 79,284	$ 210,263	$ 155,128
Tenant reinsurance	12,110	9,008	22,331	17,565
Management fees	6,796	6,659	12,974	13,245
Total revenues	126,246	94,951	245,568	185,938
Expenses:
Property operations	33,462	26,012	67,899	52,608
Tenant reinsurance	2,202	1,424	4,112	3,272
Acquisition related costs	683	469	1,135	1,078
General and administrative	13,739	12,545	26,508	25,185
Depreciation and amortization	22,785	16,626	45,810	33,150
Total expenses	72,871	57,076	145,464	115,293
Income from operations	53,375	37,875	100,104	70,645
Gain on sale of real estate assets	800		800
Interest expense	(18,362)	(15,854)	(35,728)	(33,925)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	(113)		(113)	(444)
Interest income	133	448	317	723
Interest income on note receivable from Preferred Operating Partnership unit holder	1,212	1,212	2,425	2,425
Income before equity in earnings of unconsolidated real estate ventures and income tax expense	37,045	23,681	67,805	39,424
Equity in earnings of unconsolidated real estate ventures	2,914	2,698	5,537	4,994
Equity in earnings of unconsolidated real estate ventures - gain on sale of real estate assets and purchase of joint venture partners' interests			2,556	5,429
Income tax expense	(2,858)	(1,634)	(4,866)	(2,584)
Net income	37,101	24,745	71,032	47,263
Net income allocated to Preferred Operating Partnership noncontrolling interests	(1,745)	(1,654)	(3,462)	(3,303)
Net income allocated to Operating Partnership and other noncontrolling interests	(890)	(678)	(1,679)	(1,333)
Net income attributable to common stockholders	$ 34,466	$ 22,413	$ 65,891	$ 42,627
Net income per common share
Basic (in dollars per share)	$ 0.31	$ 0.22	$ 0.59	$ 0.43
Diluted (in dollars per share)	$ 0.31	$ 0.22	$ 0.59	$ 0.43
Weighted average number of shares
Basic (in shares)	111,137,437	102,107,535	110,974,504	98,497,788
Diluted (in shares)	115,359,245	106,653,965	115,237,500	103,063,565
Cash dividends paid per common share (in dollars per share)	$ 0.40	$ 0.20	$ 0.65	$ 0.40