Risk Management and Use of Derivative Financial Instruments - Terms and Fair Values of Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivatives Fair Value [Line Items]
Notional Amount	$ 301,548	$ 301,548
3.718% Interest Rate Swap Maturing October 8, 2022 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Notional Amount	$ 250,000	250,000
Derivative, Fixed Interest Rate	2.868%
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 7,008	5,694
3.300% Interest Rate Swap Maturing January 30, 2021 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Notional Amount	$ 25,774	25,774
Derivative, Fixed Interest Rate	3.30%
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 292	25
3.090% Interest Rate Swap Maturing October 30, 2019 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Notional Amount	$ 25,774	25,774
Derivative, Fixed Interest Rate	3.09%
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 183	$ 59