Segment Information - Reconciliation of Consolidated Net Operating Income to Consolidated Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting [Abstract]
Consolidated net operating income									$ 364,544	$ 361,017	$ 340,441
Less:
Interest expense									(110,717)	(124,329)	(121,937)
Interest expense - amortization of deferred financing costs									(4,557)	(5,148)	(4,676)
Interest expense - financing obligation									(1,237)	(1,144)	(972)
Depreciation and amortization									(219,029)	(208,569)	(197,021)
General and administrative expenses									(29,406)	(26,779)	(27,628)
Equity in income (loss) of Real Estate Ventures									(811)	(790)	3,664
Provision for impairment									(82,208)	(1,765)	0
Plus:
Interest income									1,224	3,974	1,044
Tax credit transaction income									19,955	11,853	11,853
Recognized hedge activity									0	(828)	0
Net gain from remeasurement of investments in real estate ventures									758	458	6,866
Net gain on disposition of real estate									20,496	4,901	0
Net gain (loss) on sale of undepreciated real estate									3,019	1,184	(137)
Net gain (loss) on real estate venture transactions									7,229	(417)	29,604
Loss on early extinguishment of debt									0	(7,594)	(2,119)
Income (loss) from continuing operations									(30,740)	6,024	38,982
Income from discontinued operations									0	918	4,207
Net income (loss)	$ (62,700)	$ 20,308	$ 3,058	$ 8,594	$ (1,869)	$ 8,882	$ 2,174	$ (2,245)	$ (30,740)	$ 6,942	$ 43,189