Segments Disclosure - Schedule of Each Reportable Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Revenues
Rental income	$ 146,470	$ 435,630
Tenant reimbursement income	14,405	39,956
Fee and other income	6,851	16,294
Total revenues	167,726	491,880
Total expenses	141,159	444,921
Operating income (loss)	26,567	46,959
Income from real estate fund investments	10,933	30,226
Income from unconsolidated joint ventures	1,458	4,444
Unrealized gains on interest rate swaps	15,772	49,497
Interest and other (loss) income, net	(1,763)	(397)
Interest and debt expense	(42,821)	(126,945)
Net income before income taxes	10,146	3,784
Income tax benefit (expense)	(789)	(2,706)
Net income	9,357	1,078
Depreciation and amortization	70,654	223,658
General and administrative	6,666	28,412
Interest and debt expense	42,821	126,945
Transfer taxes due in connection with the sale of shares by a former joint venture partner		5,872
Acquisition and transaction related costs	485	3,960
Income tax (expense) benefit	789	2,706
Net Operating Income from unconsolidated joint ventures	4,303	12,362
Income from real estate fund investments	(10,933)	(30,226)
Income from unconsolidated joint ventures	(1,458)	(4,444)
Fee income	(2,085)	(5,400)
Unrealized (gains) losses on interest rate swaps	(15,772)	(49,497)
Interest and other (loss) income, net	1,763	397
Net Operating Income	106,590	315,823
Owned Properties [Member]
Revenues
Rental income	145,711	433,537
Tenant reimbursement income	14,405	39,956
Fee and other income	4,767	10,890
Total revenues	164,883	484,383
Total expenses	134,667	408,319
Operating income (loss)	30,216	76,064
Income from unconsolidated joint ventures	1,433	4,358
Unrealized gains on interest rate swaps	15,772	49,497
Interest and other (loss) income, net	119	304
Interest and debt expense	(41,811)	(120,684)
Net income before income taxes	5,729	9,539
Income tax benefit (expense)	275	282
Net income	6,004	9,821
Depreciation and amortization	70,366	222,822
Interest and debt expense	41,811	120,684
Income tax (expense) benefit	(275)	(282)
Net Operating Income from unconsolidated joint ventures	4,210	12,084
Income from unconsolidated joint ventures	(1,433)	(4,358)
Unrealized (gains) losses on interest rate swaps	(15,772)	(49,497)
Interest and other (loss) income, net	(119)	(304)
Net Operating Income	104,792	310,970
Other [Member]
Revenues
Rental income	759	2,093
Fee and other income	2,084	5,404
Total revenues	2,843	7,497
Total expenses	6,492	36,602
Operating income (loss)	(3,649)	(29,105)
Income from real estate fund investments	10,933	30,226
Income from unconsolidated joint ventures	25	86
Interest and other (loss) income, net	(1,882)	(701)
Interest and debt expense	(1,010)	(6,261)
Net income before income taxes	4,417	(5,755)
Income tax benefit (expense)	(1,064)	(2,988)
Net income	3,353	(8,743)
Depreciation and amortization	288	836
General and administrative	6,666	28,412
Interest and debt expense	1,010	6,261
Transfer taxes due in connection with the sale of shares by a former joint venture partner		5,872
Acquisition and transaction related costs	485	3,960
Income tax (expense) benefit	1,064	2,988
Net Operating Income from unconsolidated joint ventures	93	278
Income from real estate fund investments	(10,933)	(30,226)
Income from unconsolidated joint ventures	(25)	(86)
Fee income	(2,085)	(5,400)
Interest and other (loss) income, net	1,882	701
Net Operating Income	$ 1,798	$ 4,853