Accounting for the Impairment or Disposal of Long-Lived Assets - Results of Operations for the Properties Held for Sale and Disposed (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Property, Plant and Equipment Impairment or Disposal [Abstract]
Revenues	$ 576,000	$ 16,886,000	$ 10,235,000	$ 39,095,000
Operating expenses	(297,000)	(7,033,000)	(4,464,000)	(16,670,000)
Interest and other income	2,000	58,000	30,000	154,000
Interest expense	(77,000)	(2,845,000)	(1,706,000)	(6,172,000)
Depreciation and amortization	(88,000)	(3,195,000)	(245,000)	(8,742,000)
Income before property dispositions	116,000	3,871,000	3,850,000	7,665,000
Gain on property dispositions	2,981,000	50,157,000	4,045,000	50,627,000
Net income	3,097,000	54,028,000	7,895,000	58,292,000
Proceeds from Sale of Property, Plant, and Equipment	$ 204,300,000	$ 266,000,000	$ 210,800,000	$ 269,700,000