Acquisition, Development, Construction and Disposition Activity (Income from Discontinued Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended						12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Acquisition, Development, Construction and Disposition Activity [Abstract]
Property revenue	$ 1,255	$ 2,179	$ 2,138	$ 1,210	$ 2,085	$ 2,030	$ 9,191	$ 21,649	$ 29,545
Property operating and maintenance							4,233	10,351	14,302
Depreciation and amortization							1,779	5,606	8,162
Total expenses							6,012	15,957	22,464
Operating income							3,179	5,692	7,081
Interest expense							0	(1,811)	(3,439)
Operating income, net of interest expense							3,179	3,881	3,642
Gain on disposition of properties							52,828	26,849	14,597
Income from discontinued operations							$ 56,007	$ 30,730	$ 18,239