SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 segment	Mar. 31, 2013	Dec. 31, 2013
SEGMENT INFORMATION
Number of reportable segments	3
Balance Sheet
Investment in unconsolidated real estate ventures	$ 89,326		$ 88,125
Total assets	4,123,491		3,977,140
Statement of Operations
Total revenues	152,180	119,322
Operating expenses, including depreciation and amortization	91,782	72,593
Income (loss) from operations	60,398	46,729
Interest expense	(19,598)	(17,366)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	(662)
Interest income	269	184
Interest income on note receivable from Preferred Operating Partnership unit holder	1,213	1,213
Equity in earnings of unconsolidated real estate ventures	2,419	2,623
Equity in earnings of unconsolidated real estate ventures - purchase of partners' interests		2,556
Income tax expense	(2,830)	(2,008)
Net income (loss)	41,209	33,931
Depreciation and amortization expense
Depreciation and amortization expense	28,375	23,025
Statement of Cash Flows
Acquisition of real estate assets	(256,759)	(18,754)
Rental operations
Balance Sheet
Investment in unconsolidated real estate ventures	89,326		88,125
Total assets	3,873,654		3,641,746
Statement of Operations
Total revenues	132,001	102,923
Operating expenses, including depreciation and amortization	69,942	55,968
Income (loss) from operations	62,059	46,955
Interest expense	(19,310)	(16,980)
Equity in earnings of unconsolidated real estate ventures	2,419	2,623
Equity in earnings of unconsolidated real estate ventures - purchase of partners' interests		2,556
Income tax expense	1,419	1,009
Net income (loss)	46,587	36,163
Depreciation and amortization expense
Depreciation and amortization expense	26,460	21,531
Tenant reinsurance
Balance Sheet
Total assets	31,628		34,393
Statement of Operations
Total revenues	13,463	10,221
Operating expenses, including depreciation and amortization	2,567	1,910
Income (loss) from operations	10,896	8,311
Interest income	4	4
Income tax expense	(3,815)	(2,866)
Net income (loss)	7,085	5,449
Property management, acquisition and development
Balance Sheet
Total assets	218,209		301,001
Statement of Operations
Total revenues	6,716	6,178
Operating expenses, including depreciation and amortization	19,273	14,715
Income (loss) from operations	(12,557)	(8,537)
Interest expense	(288)	(386)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	(662)
Interest income	265	180
Interest income on note receivable from Preferred Operating Partnership unit holder	1,213	1,213
Income tax expense	(434)	(151)
Net income (loss)	(12,463)	(7,681)
Depreciation and amortization expense
Depreciation and amortization expense	1,915	1,494
Statement of Cash Flows
Acquisition of real estate assets	$ (256,759)	$ (18,754)