SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Noncontrolling Interest (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance				$ 417,352,000					$ 417,352,000
Net income for the period January 1 through December 31, 2014									81,082,000	4,525,000	50,230,000
Conversion of 136,128 OP Units to Common Shares by limited partners of the Operating Partnership									0	0	0
Issuance of OP Units to acquire real estate									44,051,000	33,300,000	2,279,000
Other comprehensive income - unrealized loss on valuation of swap agreements									(9,061,000)	3,610,000	(3,519,000)
Reclassification of realized interest on swap agreements									3,776,000	2,892,000	2,268,000
Noncontrolling interest contributions									57,969,000	49,324,000	172,228,000
Noncontrolling interest distributions and other reductions									(218,152,000)	(87,688,000)	(160,663,000)
Employee Long-term Incentive Plan Unit Awards									8,460,000	7,672,000	6,691,000
Balance	380,416,000				417,352,000				380,416,000	417,352,000
Distributions declared (in dollars per share)	$ 0.54	$ 0.23	$ 0.23	$ 0.23	$ 0.23	$ 0.21	$ 0.21	$ 0.21	$ 1.23	$ 0.86	$ 0.72
Limited partners' capital account, units issued and converted (in shares)	136,128								136,128
Units converted from Series A Preferred OP Units (in shares)	185,600								185,600
Denominator for Series A Preferred OP Unit conversion	7.50								7.50
LTIP Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
LTIP units outstanding (in shares)	1,719,206				1,368,086				1,719,206	1,368,086
Series A Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Per unit conversion amount, Series A Preferred OP Units (in dollars per unit)	22.50								22.50
Per unit conversion annual rate, Series A Preferred OP Units	9.00%								9.00%
Limited partners' capital account, units issued and converted (in shares)	1,392								1,392
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of 136,128 OP Units to Common Shares by limited partners of the Operating Partnership									(3,181,000)	(1,548,000)	(5,880,000)
Issuance of OP Units to acquire real estate									44,051,000	33,300,000	2,279,000
Other comprehensive income - unrealized loss on valuation of swap agreements									(1,247,000)	69,000	(1,704,000)
Reclassification of realized interest on swap agreements									1,099,000	994,000	847,000
Noncontrolling interest contributions									57,969,000	49,324,000	172,228,000
Noncontrolling interest distributions and other reductions									(218,152,000)	(87,688,000)	(160,663,000)
Employee Long-term Incentive Plan Unit Awards									6,528,000	6,530,000	6,025,000
Noncontrolling Interests | Partially-Owned Affiliates [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance				368,404,000					368,404,000
Distributions declared of $1.23 per Common OP Unit									0
Net income for the period January 1 through December 31, 2014									77,878,000
Conversion of 136,128 OP Units to Common Shares by limited partners of the Operating Partnership									0
Issuance of OP Units to acquire real estate									0
Other comprehensive income - unrealized loss on valuation of swap agreements									(902,000)
Reclassification of realized interest on swap agreements									984,000
Noncontrolling interest contributions									57,969,000
Noncontrolling interest distributions and other reductions									(218,152,000)
Employee Long-term Incentive Plan Unit Awards									0
Balance	286,181,000								286,181,000
Operating Partnership, as General Partner or Managing Member [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Series A Preferred OP Units (in shares)	2,988,277				1,457,467				2,988,277	1,457,467
Operating Partnership, as General Partner or Managing Member [Member] | Series A Preferred Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Series A Preferred OP Units (in shares)	188				188				188	188	188
Limited partners' capital account, value per unit (in dollars per unit)	1,000				1,000				1,000	1,000
Operating Partnership, as General Partner or Managing Member [Member] | Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance				48,948,000					48,948,000
Distributions declared of $1.23 per Common OP Unit									(5,085,000)
Net income for the period January 1 through December 31, 2014									3,204,000
Conversion of 136,128 OP Units to Common Shares by limited partners of the Operating Partnership									(3,181,000)
Issuance of OP Units to acquire real estate									44,051,000
Other comprehensive income - unrealized loss on valuation of swap agreements									(345,000)
Reclassification of realized interest on swap agreements									115,000
Noncontrolling interest contributions									0
Noncontrolling interest distributions and other reductions									0
Employee Long-term Incentive Plan Unit Awards									6,528,000
Balance	$ 94,235,000								$ 94,235,000