Condensed Consolidating Financial Information (Schedule Of Condensed Consolidating Balance Sheet) (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	$ 132,505,000	$ 122,878,000
Total property and equipment, net	2,568,425,000	2,635,810,000
Investment in subsidiaries	0	0
Other assets	20,909,000	19,616,000
Total Assets	2,721,839,000	2,778,304,000
Current liabilities	503,531,000	372,822,000
Long-term liabilities	1,618,982,000	1,820,323,000
Preferred Stock	172,858,000	214,262,000
Total shareholders’ equity	426,468,000	370,897,000
Total Liabilities and Shareholders’ Equity	2,721,839,000	2,778,304,000
Eliminations [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	(3,116,164,000)	(3,424,288,000)
Total property and equipment, net	(3,847,000)	(3,878,000)
Investment in subsidiaries	743,363,000	999,793,000
Other assets	0	0
Total Assets	(2,376,648,000)	(2,428,373,000)
Current liabilities	(3,119,185,000)	(3,427,308,000)
Long-term liabilities	15,879,000	15,879,000
Preferred Stock	0	0
Total shareholders’ equity	726,658,000	983,056,000
Total Liabilities and Shareholders’ Equity	(2,376,648,000)	(2,428,373,000)
Parent Company [Member] | Reportable Legal Entities [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	3,128,244,000	3,441,633,000
Total property and equipment, net	6,445,000	5,953,000
Investment in subsidiaries	(743,363,000)	(999,793,000)
Other assets	8,630,000	9,270,000
Total Assets	2,399,956,000	2,457,063,000
Current liabilities	257,137,000	165,701,000
Long-term liabilities	1,526,788,000	1,689,466,000
Preferred Stock	172,858,000	214,262,000
Total shareholders’ equity	443,173,000	387,634,000
Total Liabilities and Shareholders’ Equity	2,399,956,000	2,457,063,000
Combined Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	120,425,000	105,533,000
Total property and equipment, net	2,562,799,000	2,630,707,000
Investment in subsidiaries	0	0
Other assets	12,279,000	10,346,000
Total Assets	2,695,503,000	2,746,586,000
Current liabilities	3,362,551,000	3,631,401,000
Long-term liabilities	76,315,000	114,978,000
Preferred Stock	0	0
Total shareholders’ equity	(743,363,000)	(999,793,000)
Total Liabilities and Shareholders’ Equity	2,695,503,000	2,746,586,000
Combined Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Total current assets	0	0
Total property and equipment, net	3,028,000	3,028,000
Investment in subsidiaries	0	0
Other assets	0	0
Total Assets	3,028,000	3,028,000
Current liabilities	3,028,000	3,028,000
Long-term liabilities	0	0
Preferred Stock	0	0
Total shareholders’ equity	0	0
Total Liabilities and Shareholders’ Equity	$ 3,028,000	$ 3,028,000