Operating Expenses (Schedule of Selling, General and Administrative Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating Expenses [Abstract]
Employee compensation expenses	$ 44,455	$ 44,011
Buildings, facilities and technology expenses	12,270	11,236
Travel, advertising and promotion expense	6,586	5,530
Professional fees	3,100	2,766
Other SG&A expenses	4,164	3,567
Total selling, general and administrative expenses	$ 70,575	$ 67,110