Operating Expenses (Schedule of Selling, General and Administrative Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Expenses [Abstract]
Employee compensation expenses	$ 61,464	$ 63,293
Buildings, facilities and technology expenses	15,915	15,273
Travel, advertising and promotion expenses	9,142	9,719
Professional fees	4,075	4,267
Other SG&A expenses	4,588	4,918
Total selling, general and administrative expenses	$ 95,184	$ 97,470