Notes and Bonds Payable - Mortgage Notes (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Notes and bonds payable	$ 1,403,692,000	[1]	$ 1,348,459,000	[1]
Mortgage notes payable [Member] | 5.000%-7.63% Mortgage Notes Payable [Member]
Debt Instrument [Line Items]
Mortgage notes	172,530,000		166,684,000
Unamortized premium	3,205,000		2,708,000
Unaccreted discount	(2,468,000)		(3,596,000)
Notes and bonds payable	$ 173,267,000		$ 165,796,000

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