Business Segments (Principal Geographical Areas) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Principal Geographical Areas Information
Revenues	$ 1,183,284	$ 1,123,137	$ 1,120,085	$ 1,028,156	$ 1,193,068	$ 1,199,505	$ 1,247,274	$ 1,117,361	$ 4,454,662	$ 4,757,208	$ 4,973,076
Assets	4,387,752				4,264,123				4,387,752	4,264,123
United States
Principal Geographical Areas Information
Revenues									4,180,206	4,613,644	4,802,393
Assets	4,225,143				4,093,673				4,225,143	4,093,673
Foreign and U.S. Territories [Member]
Principal Geographical Areas Information
Revenues									274,456	143,564	$ 170,683
Assets	$ 162,609				$ 170,450				$ 162,609	$ 170,450