Real Estate and Accumulated Depreciation (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Real Estate and Accumulated Depreciation [Line Items]
Aggregate cost of real estate owned for federal income tax purposes	$ 677,000,000
Balance at Beginning of Year	429,431,000	799,506,000	781,664,000
Amounts Capitalized	21,058,000	28,309,000	32,215,000
Impairments	(2,551,000)	(377,270,000)	(4,297,000)
Amounts Retired or Adjusted	(29,741,000)	(21,114,000)	(10,076,000)
Balance at Close of Period	418,197,000	429,431,000	799,506,000
Balance at Beginning of Year	44,489,000	41,992,000	35,000,000
Depreciation Expense	7,494,000	12,215,000	9,453,000
Amounts Retired or Adjusted	(2,211,000)	(9,718,000)	(2,461,000)
Balance at Close of Period	$ 49,772,000	$ 44,489,000	$ 41,992,000