Business Segments and Geographic Information (Geographic Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Geographical Information
Revenues	$ 500,127	$ 469,866	$ 445,945	$ 427,369	$ 427,740	$ 457,900	$ 412,843	$ 393,137	$ 1,843,307	$ 1,691,620	$ 1,522,074
Property and equipment, net	1,916,386				1,772,166				1,916,386	1,772,166	1,727,798
U.S. operations
Geographical Information
Revenues									1,581,811	1,438,144	1,314,425
Property and equipment, net	1,910,378				1,765,391				1,910,378	1,765,391	1,721,761
Australia operations
Geographical Information
Revenues									237,731	210,577	158,028
Property and equipment, net	5,871				5,923				5,871	5,923	4,828
South African operations
Geographical Information
Revenues									14,964	16,831	17,992
Property and equipment, net	90				127				90	127	158
United Kingdom operations
Geographical Information
Revenues									8,801	26,068	31,629
Property and equipment, net	$ 47				$ 725				$ 47	$ 725	$ 1,051