Business Segments and Geographic Information (Geographic Information) (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
Geographical Information
Revenues	$ 566,579	$ 554,376	$ 548,350	$ 510,185	$ 500,127	$ 469,866	$ 445,945	$ 427,369	$ 2,179,490	$ 1,843,307	$ 1,691,620
Property and equipment, net	1,897,241				1,916,386				1,897,241	1,916,386	1,772,166
U.S. operations
Geographical Information
Revenues									1,770,273	1,581,811	1,438,144
Property and equipment, net	1,887,043				1,910,378				1,887,043	1,910,378	1,765,391
Australia operations
Geographical Information
Revenues									388,361	237,731	210,577
Property and equipment, net	10,053				5,871				10,053	5,871	5,923
South African operations
Geographical Information
Revenues									13,658	14,964	16,831
Property and equipment, net	145				90				145	90	127
United Kingdom operations
Geographical Information
Revenues									7,198	8,801	26,068
Property and equipment, net	$ 0				$ 47				$ 0	$ 47	$ 725