Segment Information (Reconciliation of Consolidated Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015		Jun. 30, 2014
Other income (expense):
Depreciation and amortization	$ (50,930)	$ (52,587)	$ (102,041)		$ (105,157)
General and administrative expenses	(6,791)	(6,005)	(15,427)		(14,186)
Interest income	313	385	1,063		770
Interest expense	(27,895)	(31,512)	(56,071)		(63,356)
Interest expense — amortization of deferred financing costs	(1,288)	(1,197)	(2,367)		(2,386)
Interest expense — financing obligation	(324)	(316)	(610)		(588)
Equity in loss of Real Estate Ventures	(873)	(489)	(742)		(247)
Net gain on disposition of real estate	1,571	0	10,590	[1]	0
Net gain (loss) on sale of undepreciated real estate	0	(3)	0		1,184
Net gain from remeasurement of investments in real estate ventures	758	458	758		458
Loss on real estate venture transactions	0	(282)	0		(417)
Provision for impairment on assets held for sale/sold	(782)	0	(2,508)		0
Income (Loss) from continuing operations	3,058	1,245	11,652		(992)
Total discontinued operations	0	929	0		921
Net income	3,058	2,174	11,652		(71)
Operating Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Consolidated net operating income	89,299	92,793	179,007		182,933
Other income (expense):
Depreciation and amortization	(50,930)	(52,587)	(102,041)		(105,157)
General and administrative expenses	(6,791)	(6,005)	(15,427)		(14,186)
Interest income	313	385	1,063		770
Interest expense	(27,895)	(31,512)	(56,071)		(63,356)
Interest expense — amortization of deferred financing costs	(1,288)	(1,197)	(2,367)		(2,386)
Interest expense — financing obligation	(324)	(316)	(610)		(588)
Equity in loss of Real Estate Ventures	(873)	(489)	(742)		(247)
Net gain on disposition of real estate	1,571	0	10,590		0
Net gain (loss) on sale of undepreciated real estate	0	(3)	0		1,184
Net gain from remeasurement of investments in real estate ventures	758	458	758		458
Loss on real estate venture transactions	0	(282)	0		(417)
Provision for impairment on assets held for sale/sold	(782)	0	(2,508)		0
Income (Loss) from continuing operations	3,058	1,245	11,652		(992)
Total discontinued operations	0	929	0		921
Net income	$ 3,058	$ 2,174	$ 11,652		$ (71)

[1] Gain/(Loss) on Sale is net of closing and other transaction related costs.