Reportable Segments Reportable Segments (Revenue Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Document Fiscal Year Focus			2015
Rental property operating expenses	$ (41,331)	$ (38,685)	$ (120,672)	$ (109,501)
Total consolidated revenues	98,146	89,098	288,025	255,326
Total Segment [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	60,816	55,112	179,643	156,419	$ 156,419	$ 179,643
Residential Lot Sales Net of Cost of Sales Including Gain on Sale of Undepreciated Investment Properties	3,016	82	3,502	1,615	1,615
Fee income, Net of Reimbursed Expenses	1,686	1,802	5,206	6,165	6,165
Other Income	845	$ 399	$ 1,490	4,563	4,563
Rental property operating expenses				38,685	(109,501)
Plus residential lot, multi-family unit and outparcel cost of sales	0			55	(325)	0
Net operating income in joint venture	(6,132)			(6,601)	(19,748)	(18,102)
Net sales of joint ventures	(2,038)			0	(47)	(2,280)
Net operating income from discontinued operations not included in revenues	0			(341)	(1,798)	14
Discontinued Operations Other Income	129			14	29	479
Termination Fees in Discontinues Operations and in Joint Ventures	(271)			0	(74)	(419)
Residential Lot Multi Family Unit Tract and Outparcel Sales Net of Cost of Sales Including Gain on Sale of Undepreciated Investment Properties	(978)			(81)	(1,566)	(1,222)
Total consolidated revenues	$ 98,146			$ 89,098	$ 255,326	$ 288,025