Operating Expenses (Schedule of Selling, General and Administrative Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Expenses
Employee compensation expenses	$ 246,028	$ 249,115	$ 208,370
Buildings, facilities and technology expenses	61,177	60,930	53,151
Travel, advertising and promotion expenses	38,248	36,728	30,440
Professional fees	15,572	16,768	13,522
Other SG&A expenses	21,364	19,135	17,787
Total selling, general and administrative expenses	$ 382,389	$ 382,676	$ 323,270