Summary of Significant Accounting Policies and Procedures and Recent Accounting Pronouncements (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012 property	Dec. 31, 2011	Dec. 31, 2010	Aug. 31, 2011
Reconciliation of the denominator of the basic net income per common share computation to the denominator of the diluted net income per common share computation
Weighted average shares used for the basic net income per share computation	132,817,472	126,142,696	105,869,637
Incremental shares from share-based compensation	67,461	46,703	73,084
Adjusted weighted average shares used for diluted net income per share computation	132,884,933	126,189,399	105,942,721
Unvested shares from share-based compensation that were anti-dilutive	17,570	13,020	87,600
Discontinued Operations
Number of investment properties classified as held for sale, reported as discontinued operations	14
Income from discontinued operations
Gain on sales of investment properties	$ 9,873,000	$ 5,193,000	$ 8,676,000
Rental revenue	7,938,000	11,881,000	13,071,000
Other revenue	243,000	93,000	32,000
Depreciation and amortization	(1,710,000)	(3,305,000)	(4,508,000)
Property expenses	(1,649,000)	(1,902,000)	(2,463,000)
Provisions for impairment	(2,335,000)	(395,000)	(171,000)
Crest's income from discontinued operations	821,000	842,000	946,000
Income from discontinued operations	13,181,000	12,407,000	15,583,000
Per common share, basic and diluted (in dollars per share)	$ 0.10	$ 0.10	$ 0.15
Revenue Recognition and Accounts Receivable
Allowance for doubtful accounts	448,000	507,000
Non-operating interest earned from notes receivable and investments in money market	1,200,000	502,000	96,000
Net decrease to rental revenue
2013	(1,314,000)
2014	(1,399,000)
2015	(1,345,000)
2016	(1,341,000)
2017	(1,332,000)
Thereafter	(2,610,000)
Totals	(9,341,000)
Increase to amortization expense
2013	22,110,000
2014	21,899,000
2015	21,105,000
2016	21,026,000
2017	20,475,000
Thereafter	99,698,000
Totals	$ 206,313,000
Par Value Change
Par value of common stock, before change (in dollars per share)				$ 1.00
Par value of preferred stock, before change (in dollars per share)				$ 1.00
Par value of common stock (in dollars per share)	$ 0.01	$ 0.01
Par value of preferred stock (in dollars per share)	$ 0.01	$ 0.01