Operating Expenses (Schedule of Selling, General and Administrative Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Expenses [Abstract]
Employee compensation expenses	$ 249,115	$ 208,370	$ 180,929
Buildings, facilities and technology expenses	60,930	53,151	49,219
Travel, advertising and promotion expenses	36,728	30,440	24,384
Professional fees	16,768	13,522	13,344
Other SG&A expenses	19,135	17,787	15,653
Total selling, general and administrative expenses	$ 382,676	$ 323,270	$ 283,529