Operating Expenses (Schedule of Direct Operating Expenses) (Details) - Service Revenues [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Ancillary and logistical service expenses	$ 66,576	$ 54,176	$ 47,234
Employee compensation expenses	41,391	35,440	27,856
Buildings, facilities and technology expenses	9,477	8,359	7,966
Travel, advertising and promotion expenses	27,606	23,994	23,688
Other costs of services	14,008	11,220	6,552
Total direct expenses	$ 159,058	$ 133,189	$ 113,296