Fair Value of Financial Instruments (Details) (USD $)	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Fair value and carrying values for notes and bonds payable, mortgage notes receivable and notes receivable
Notes and bonds payable	$ 1,293,044,000	[1]	$ 1,393,537,000	[1]
Mortgage notes receivable	162,191,000	[2],[3]	97,381,000	[2],[3]	36,599,000	[2]	31,008,000
Notes receivable, net of allowances	100,000	[3]	300,000	[3]
Notes and bonds payable, Fair Value	1,437,200,000	[1]	1,534,300,000	[1]
Mortgage notes receivable, Fair Value	158,300,000	[3]	95,500,000	[3]
Notes receivable, net of allowances, Fair Value	$ 100,000	[3]	$ 300,000	[3]

[1] Level 3 - Fair value derived from valuation techniques in which one of more significant inputs or significant value drivers are unobservable.

[2] Total mortgage notes as of December 31, 2012 had an aggregate total cost of $162.2 million for federal income tax purposes.

[3] Level 2 - Fair value based on quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-driven valuations in which significant inputs and significant value drivers are observable in active markets.