Business Segments and Geographic Information (Geographic Information) (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
Geographical Information
Revenues	$ 621,710	$ 631,579	$ 613,966	$ 610,667	$ 599,430	$ 583,530	$ 583,509	$ 564,917	$ 2,477,922	$ 2,331,386	$ 2,263,420
Property and equipment, net	2,144,722				2,158,610				2,144,722	2,158,610	2,078,123
U.S. operations
Geographical Information
Revenues									2,216,401	2,073,286	1,952,210
Property and equipment, net	2,131,877				2,145,197				2,131,877	2,145,197	2,061,711
Australia operations
Geographical Information
Revenues									235,462	231,164	285,702
Property and equipment, net	12,215				13,006				12,215	13,006	16,281
South African operations
Geographical Information
Revenues									18,779	19,806	18,251
Property and equipment, net	182				88				182	88	131
United Kingdom operations
Geographical Information
Revenues									7,280	7,130	7,257
Property and equipment, net	$ 448				$ 319				$ 448	$ 319	$ 0