Operating Expenses (Schedule of Selling, General and Administrative Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Expenses [Abstract]
Employee compensation expenses	$ 63,293	$ 44,455
Buildings, facilities and technology expenses	15,273	12,270
Travel, advertising and promotion expenses	9,719	6,586
Professional fees	4,267	3,100
Other SG&A expenses	4,918	4,164
Total selling, general and administrative expenses	$ 97,470	$ 70,575