Operating expenses (Schedule of Direct Operating Expenses) (Details) - Service Revenue [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Ancillary and logistical service expenses	$ 59,982	$ 59,252	$ 66,576
Employee compensation expenses	47,745	50,093	41,391
Buildings, facilities and technology expenses	9,886	7,865	9,477
Travel, advertising and promotion expenses	22,636	31,652	27,606
Other costs of services	17,047	16,115	14,008
Total direct expenses	$ 157,296	$ 164,977	$ 159,058