Fair Value Measurements (Details) - Recurring - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	$ 142,360	$ 211,922
Restricted cash and cash equivalents	20,880	21,935
Derivative Asset	0	0
Total	163,240	233,857
Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents	0	0
Restricted cash and cash equivalents	0	0
Derivative Asset	7,329	3,254
Total	7,329	3,254
Significant Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Restricted cash and cash equivalents	0	0
Derivative Asset	0	0
Total	0	0
Estimate of Fair Value Measurement [Member]
Assets:
Cash and cash equivalents	142,360	211,922
Restricted cash and cash equivalents	20,880	21,935
Derivative Asset	7,329	3,254
Total	$ 170,569	$ 237,111