Schedule III - Real Estate And Accumulated Depreciation (Changes In Accumulated Depreciation) (Details) (USD $)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule III - Real Estate And Accumulated Depreciation [Abstract]
Balance, Beginning of period	$ 1,292,924,000	$ 1,149,056,000	$ 981,049,000
Depreciation	171,009,000	166,867,000	170,480,000
Real Estate sold	(18,877,000)	(22,999,000)	(2,473,000)
Transferred to held for sale	(12,257,000)
Balance, end of period	1,432,799,000	1,292,924,000	1,149,056,000
Aggregate cost for federal income tax purposes		$ 5,000,000,000

Decreases or increases in accumulated depreciation for the period other than deductions attributed to real estate sold or written-off.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 970

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-28.FN4)

-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule III

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 28

-Article 12

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule III)

-URI http://asc.fasb.org/extlink&oid=6882300&loc=d3e5864-122674

Name:	us-gaap_RealEstateAccumulatedDepreciationOtherDeductions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration