Derivative Instruments (Interest Rate Caps) (Details) - Interest Rate Caps [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional amount	$ 79,000
Derivative assets	1,063	$ 415
Interest Rate Caps, Maturity Date, July 7, 2021, 2.50% [Member]
Derivative [Line Items]
Notional amount	$ 40,000
Cap rate	2.50%
Derivative assets	$ 533	207
Interest Rate Caps, Maturity Date, July 8, 2021, 2.50% [Member]
Derivative [Line Items]
Notional amount	$ 12,000
Cap rate	2.50%
Derivative assets	$ 160	62
Interest Rate Caps, Maturity Date, July 29, 2021, 2.50% [Member]
Derivative [Line Items]
Notional amount	$ 27,000
Cap rate	2.50%
Derivative assets	$ 370	$ 146