Notes and Bonds Payable (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Notes and bonds payable		1,403,692,000	[1]	$ 1,348,459,000	[1]
Line of Credit [Member] | Unsecured Credit Facility due 2017 [Member]
Debt Instrument [Line Items]
Notes and bonds payable		85,000,000		238,000,000
Medium-term Notes [Member] | Unsecured Term Loan Due 2019 [Member]
Debt Instrument [Line Items]
Notes and bonds payable		200,000,000		0
Contractual interest rates, basis spread on variable rate	1.45%
Mortgage notes payable [Member]
Debt Instrument [Line Items]
Contractual interest rates, minimum		5.00%
Contractual interest rates, maximum		7.60%
Mortgage notes payable [Member] | 5.000%-7.63% Mortgage Notes Payable [Member]
Debt Instrument [Line Items]
Notes and bonds payable		173,267,000		$ 165,796,000
Contractual interest rates, minimum		5.00%
Contractual interest rates, maximum		7.63%
LIBOR [Member] | Line of Credit [Member] | Unsecured Credit Facility due 2017 [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate		1.40%
LIBOR [Member] | Medium-term Notes [Member] | Unsecured Term Loan Due 2019 [Member]
Debt Instrument [Line Items]
Contractual interest rates, basis spread on variable rate		1.45%

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