Operating expenses (Schedule of Selling, General and Administrative Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating expenses
Wages, salaries and benefits	$ 77,487	$ 76,957
Share-based compensation expense	5,386	3,778
Buildings, facilities and technology expenses	20,086	17,343
Travel, advertising and promotion expenses	7,974	5,162
Professional fees	9,747	5,032
Other SG&A expenses	5,926	5,967
Total selling, general and administrative expenses	$ 126,606	$ 114,239