Business Segments (Principal Geographical Areas) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Principal Geographical Areas Information
Revenues	$ 1,177,725	$ 1,189,345	$ 1,125,275	$ 958,487	$ 1,183,284	$ 1,123,137	$ 1,120,085	$ 1,028,156	$ 4,450,832	$ 4,454,662	$ 4,757,208
Assets	4,485,777				4,387,752				4,485,777	4,387,752
United States
Principal Geographical Areas Information
Revenues									4,073,691	4,180,206	4,613,644
Assets	4,271,722				4,225,143				4,271,722	4,225,143
Foreign and U.S. Territories [Member]
Principal Geographical Areas Information
Revenues									377,141	274,456	$ 143,564
Assets	$ 214,055				$ 162,609				$ 214,055	$ 162,609