Condensed Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:
Net income	$ 197,645	$ 158,957
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	106,920	93,265
(Gain) loss on sale of property and equipment	(2,300)	(2,194)
Deferred income taxes	(7,150)	30,301
Other operating activities, net	(17,100)	(26,943)
Net cash provided by operating activities	278,015	253,386
Cash flows from investing activities:
Purchase of property and equipment	(311,993)	(229,199)
Proceeds from sale of property and equipment	19,485	9,354
Net cash used in investing activities	(292,508)	(219,845)
Cash flows from financing activities:
Principal payments under long-term debt agreements	(35,715)	(36,290)
Net proceeds (payments) from revolving line of credit	28,203	1,996
Net cash provided by (used in) financing activities	(7,512)	(34,294)
(Decrease) increase in cash and cash equivalents	(22,005)	(753)
Cash and cash equivalents at beginning of period	30,174	12,857
Cash and cash equivalents at end of period	$ 8,169	$ 12,104