Operating Expenses (Schedule of Selling, General and Administrative Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating Expenses
Employee compensation expenses	$ 60,680	$ 56,959	$ 186,033	$ 186,951
Buildings, facilities and technology expenses	14,569	15,058	45,066	45,767
Travel, advertising and promotion expenses	10,033	9,302	28,400	27,821
Professional fees	3,685	2,983	11,915	12,638
Other SG&A expenses	4,724	4,021	15,175	13,875
Total selling, general and administrative expenses	$ 93,691	$ 88,323	$ 286,589	$ 287,052