Operating Expenses (Schedule of Selling, General and Administrative Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating Expenses [Abstract]
Employee compensation expenses	$ 47,405	$ 46,989	$ 91,860	$ 91,000
Buildings, facilities and technology expenses	13,319	12,969	25,594	24,205
Travel, advertising and promotion expense	6,201	6,792	12,781	12,322
Professional fees	3,224	3,083	6,324	5,849
Other SG&A expenses	4,228	4,159	8,393	7,726
Total selling, general and administrative expenses	$ 74,377	$ 73,992	$ 144,952	$ 141,102