Operating expenses (Schedule of Direct Operating Expenses) (Details) - Service Revenue [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Ancillary and logistical service expenses	$ 16,060	$ 16,472	$ 28,818	$ 30,231
Employee compensation expenses	11,311	14,906	23,615	25,713
Buildings, facilities and technology expenses	2,076	2,172	6,115	4,306
Travel, advertising and promotion expenses	6,161	12,807	12,736	18,675
Other costs of services	3,840	3,911	7,519	7,412
Total direct expenses	$ 39,448	$ 50,268	$ 78,803	$ 86,337