Condensed Consolidating Financial Information (Schedule Of Condensed Consolidating Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Current assets	$ 148,147	$ 120,397
Property and equipment, net	1,464,147	1,310,514
Investment in subsidiaries	0	0
Other assets	92,348	96,769
TOTAL ASSETS	1,704,642	1,527,680
Current liabilities	314,702	271,320
Long-term liabilities	832,640	746,505
Shareholders' equity	557,300	509,855
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	1,704,642	1,527,680
Parent Company [Member]
Current assets	1,440,016	1,349,841
Property and equipment, net	108,699	101,015
Investment in subsidiaries	(21,347)	(58,764)
Other assets	51,012	38,853
TOTAL ASSETS	1,578,380	1,430,945
Current liabilities	171,965	150,793
Long-term liabilities	804,554	724,801
Shareholders' equity	601,861	555,351
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	1,578,380	1,430,945
Combined Guarantor Subsidiaries [Member]
Current assets	111,247	71,018
Property and equipment, net	1,234,104	1,131,672
Investment in subsidiaries	0	0
Other assets	38,499	54,062
TOTAL ASSETS	1,383,850	1,256,752
Current liabilities	1,466,599	1,368,456
Long-term liabilities	2,232	2,183
Shareholders' equity	(84,981)	(113,887)
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	1,383,850	1,256,752
Combined Non-Guarantor Subsidiaries [Member]
Current assets	1,487	3,874
Property and equipment, net	98,317	68,911
Investment in subsidiaries	0	0
Other assets	11,237	9,133
TOTAL ASSETS	111,041	81,918
Current liabilities	21,553	4,366
Long-term liabilities	25,854	22,429
Shareholders' equity	63,634	55,123
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	111,041	81,918
Eliminations [Member]
Current assets	(1,404,603)	(1,304,336)
Property and equipment, net	23,027	8,916
Investment in subsidiaries	21,347	58,764
Other assets	(8,400)	(5,279)
TOTAL ASSETS	(1,368,629)	(1,241,935)
Current liabilities	(1,345,415)	(1,252,295)
Long-term liabilities	0	(2,908)
Shareholders' equity	(23,214)	13,268
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ (1,368,629)	$ (1,241,935)