Business Segments (Principal Geographical Areas) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Principal Geographical Areas Information
Revenues	$ 1,246,599	$ 1,332,978	$ 1,308,130	$ 1,085,369	$ 1,200,830	$ 1,340,739	$ 1,312,438	$ 1,066,465	$ 4,973,076	$ 4,920,472	$ 4,492,309
Assets	4,038,620				3,861,300				4,038,620	3,861,300
United States [Member]
Principal Geographical Areas Information
Revenues									4,802,393	4,694,165	4,323,471
Assets	3,911,865				3,687,973				3,911,865	3,687,973
Foreign and U.S. Territories [Member]
Principal Geographical Areas Information
Revenues									170,683	226,307	$ 168,838
Assets	$ 126,755				$ 173,327				$ 126,755	$ 173,327