Derivative Instruments (Interest Rate Caps) (Details) - Interest Rate Caps [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Notional amount	$ 79,000
Derivative assets	415	$ 1,082
Interest Rate Caps, Maturity Date, July 7, 2021, 2.50% [Member]
Derivative [Line Items]
Notional amount	$ 40,000
Cap rate	2.50%
Derivative assets	$ 207	542
Interest Rate Caps, Maturity Date, July 8, 2021, 2.50% [Member]
Derivative [Line Items]
Notional amount	$ 12,000
Cap rate	2.50%
Derivative assets	$ 62	163
Interest Rate Caps, Maturity Date, July 29, 2021, 2.50% [Member]
Derivative [Line Items]
Notional amount	$ 27,000
Cap rate	2.50%
Derivative assets	$ 146	$ 377