Derivative Financial Instruments - Schedule of LIBOR interest rate caps (Details) - USD ($)	Dec. 31, 2018	Dec. 11, 2018	Jul. 16, 2018	Mar. 07, 2018	Dec. 31, 2017	Sep. 18, 2017	Jul. 28, 2017	Jun. 23, 2017	Feb. 07, 2017	Jun. 17, 2016	Feb. 25, 2016	Oct. 26, 2015
Derivatives
Notional Amount	$ 513,208,000				$ 401,079,000
LIBOR | Interest rate caps
Derivatives
Notional Amount		$ 50,000,000	$ 50,000,000	$ 50,000,000		$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 70,000,000	$ 75,000,000	$ 75,000,000
Strike Rate		2.75%	2.50%	2.25%		1.50%	1.50%	1.50%	1.50%	1.00%	1.50%	1.25%
Premium Paid		$ 210,000	$ 319,000	$ 310,000		$ 199,000	$ 359,000	$ 154,000	$ 187,000	$ 150,000	$ 57,000	$ 137,000