Fair Value of Financial Instruments (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Fair value and carrying values for notes and bonds payable, mortgage notes receivable and notes receivable
Notes and bonds payable	$ 1,403,692,000	[1]	$ 1,348,459,000	[1]
Mortgage notes receivable	1,900,000	[2]	125,547,000	[2]	162,191,000	97,381,000
Notes and bonds payable, Fair Value	1,438,800,000	[1]	1,380,600,000	[1]
Mortgage notes receivable, Fair Value	$ 1,900,000	[2]	$ 124,500,000	[2]

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

[2] 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.