Summary of Significant Accounting Policies (Details 2) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies [Abstract]
Prepaid tour expenses	$ 9,938	$ 9,846
Prepaid air expense	3,546	3,621
Prepaid client insurance	2,560	2,525
Prepaid marketing, commissions and other expenses	2,511	2,495
Prepaid corporate insurance	2,457	1,033
Prepaid port agent fees	840	1,022
Prepaid income taxes	809	809
Total prepaid expenses	$ 22,661	$ 21,351