SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 segment	Jun. 30, 2012	Dec. 31, 2012
SEGMENT INFORMATION
Number of reportable segments			3
Balance Sheet
Investments in unconsolidated real estate ventures	$ 101,698		$ 101,698		$ 106,313
Total assets	3,432,616		3,432,616		3,223,477
Statement of Operations
Total revenues	126,246	94,951	245,568	185,938
Operating expenses, including depreciation and amortization	72,871	57,076	145,464	115,293
Income (loss) 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
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 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
Depreciation and amortization expense
Total depreciation and amortization expense	22,785	16,626	45,810	33,150
Rental operations
Balance Sheet
Investments in unconsolidated real estate ventures	101,698		101,698		106,313
Total assets	3,024,448		3,024,448		2,981,927
Statement of Operations
Total revenues	107,340	79,284	210,263	155,128
Operating expenses, including depreciation and amortization	54,904	41,701	110,872	83,826
Income (loss) from operations	52,436	37,583	99,391	71,302
Gain on sale of real estate assets	800		800
Interest expense	(18,069)	(15,590)	(35,049)	(33,374)
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 partners' interests			2,556	5,429
Net income	38,081	24,691	73,235	48,351
Depreciation and amortization expense
Total depreciation and amortization expense	21,442	15,689	42,973	31,218
Tenant reinsurance
Balance Sheet
Total assets	34,524		34,524		27,645
Statement of Operations
Total revenues	12,110	9,008	22,331	17,565
Operating expenses, including depreciation and amortization	2,202	1,424	4,112	3,272
Income (loss) from operations	9,908	7,584	18,219	14,293
Interest income	4	3	8	6
Income tax expense	(6,379)	(2,655)	(9,245)	(5,005)
Net income	3,533	4,932	8,982	9,294
Property management, acquisition and development
Balance Sheet
Total assets	373,644		373,644		213,905
Statement of Operations
Total revenues	6,796	6,659	12,974	13,245
Operating expenses, including depreciation and amortization	15,765	13,951	30,480	28,195
Income (loss) from operations	(8,969)	(7,292)	(17,506)	(14,950)
Interest expense	(293)	(264)	(679)	(551)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	(113)		(113)	(444)
Interest income	129	445	309	717
Interest income on note receivable from Preferred Operating Partnership unit holder	1,212	1,212	2,425	2,425
Income tax expense	3,521	1,021	4,379	2,421
Net income	(4,513)	(4,878)	(11,185)	(10,382)
Depreciation and amortization expense
Total depreciation and amortization expense	$ 1,343	$ 937	$ 2,837	$ 1,932