Segment Information (Reconciliation of Consolidated Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Other income (expense):
Depreciation and amortization	$ (58,314)	$ (52,616)	$ (160,355)	$ (157,773)
General and administrative expenses	(6,127)	(5,900)	(21,554)	(20,086)
Interest income	126	528	1,189	1,298
Interest expense	(27,900)	(31,481)	(83,971)	(94,837)
Recognized hedge activity	0	(828)	0	(828)
Interest expense — amortization of deferred financing costs	(1,010)	(1,566)	(3,377)	(3,952)
Interest expense — financing obligation	(296)	(273)	(906)	(861)
Equity in loss of Real Estate Ventures	(1,093)	(486)	(1,835)	(733)
Net gain on disposition of real estate	6,083	4,698	16,673	4,698
Net gain on sale of undepreciated real estate	3,019	0	3,019	1,184
Net gain from remeasurement of investment in real estate ventures	0	0	758	458
Loss on real estate venture transactions	0	0	0	(417)
Loss on early extinguishment of debt	0	(2,606)	0	(2,606)
Provision for impairment on assets held for sale/sold	0	(1,765)	(2,508)	(1,765)
Tax credit transaction income	11,853	11,853	11,853	11,853
Income from continuing operations	20,308	8,885	31,960	7,893
Total discontinued operations	0	(3)	0	918
Net income	20,308	8,882	31,960	8,811
Operating Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Consolidated net operating income	93,967	89,327	272,974	272,260
Other income (expense):
Depreciation and amortization	(58,314)	(52,616)	(160,355)	(157,773)
General and administrative expenses	(6,127)	(5,900)	(21,554)	(20,086)
Interest income	126	528	1,189	1,298
Interest expense	(27,900)	(31,481)	(83,971)	(94,837)
Recognized hedge activity	0	(828)	0	(828)
Interest expense — amortization of deferred financing costs	(1,010)	(1,566)	(3,377)	(3,952)
Interest expense — financing obligation	(296)	(273)	(906)	(861)
Equity in loss of Real Estate Ventures	(1,093)	(486)	(1,835)	(733)
Net gain on disposition of real estate	6,083	4,698	16,673	4,698
Net gain on sale of undepreciated real estate	3,019	0	3,019	1,184
Net gain from remeasurement of investment in real estate ventures	0	0	758	458
Loss on real estate venture transactions	0	0	0	(417)
Loss on early extinguishment of debt	0	(2,606)	0	(2,606)
Provision for impairment on assets held for sale/sold	0	(1,765)	(2,508)	(1,765)
Tax credit transaction income	11,853	11,853	11,853	11,853
Income from continuing operations	20,308	8,885	31,960	7,893
Total discontinued operations	0	(3)	0	918
Net income	$ 20,308	$ 8,882	$ 31,960	$ 8,811