Schedule III - Real Estate and Accumulated Depreciation and Amortization (Parenthetical) (Detail) (USD $)	12 Months Ended
Dec. 31, 2012
Schedule Of Investments In Real Estate [Line Items]
Aggregate cost for federal income tax	546,959,000
Minimum [Member]
Schedule Of Investments In Real Estate [Line Items]
Estimated useful lives of the assets	16 years
Maximum [Member]
Schedule Of Investments In Real Estate [Line Items]
Estimated useful lives of the assets	25 years

Estimated economic life on which depreciation was computed, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: 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

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 970

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-28)

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

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Data Type:	xbrli:durationItemType
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Period Type:	duration