Risk Management and Use of Derivative Financial Instruments - Terms and Fair Values of Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivatives Fair Value [Line Items]
Notional Amount	$ 301,548	$ 328,610
3.300% Interest Rate Swap Maturing January 30, 2021 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Notional Amount	$ 25,774	25,774
Derivative, Fixed Interest Rate	3.30%
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		(300)
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 25
3.090% Interest Rate Swap Maturing October 30, 2019 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Notional Amount	$ 25,774	25,774
Derivative, Fixed Interest Rate	3.09%
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		(214)
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 59
2.750% Interest Rate Swap Maturing September 30, 2017 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Notional Amount		$ 27,062
Derivative, Fixed Interest Rate		2.75%
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		$ (83)
3.718% Interest Rate Swap Maturing October 8, 2022 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative, Fixed Interest Rate	3.718%
Derivative Asset, Notional Amount	$ 250,000	250,000
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 5,694	$ 3,733