Derivative Financial Instruments Derivative Financial Instruments - Schedule of LIBOR interest rate caps (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018	Dec. 11, 2018	Jul. 16, 2018	Mar. 07, 2018	Nov. 28, 2017	Sep. 18, 2017	Jun. 23, 2017	Feb. 07, 2017
Derivative [Line Items]
Notional Amount	$ 462,977,000	$ 513,208,000
Interest Rate Caps | LIBOR
Derivative [Line Items]
Notional Amount			$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000
Strike Rate			2.75%	2.50%	2.25%	1.50%	1.50%	1.50%	1.50%
Premium Paid			$ 210,000	$ 319,000	$ 310,000	$ 359,000	$ 199,000	$ 154,000	$ 187,000