Condensed Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 109,333	$ 65,792
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	53,481	50,287
(Gain) loss on sale of property and equipment	364	77
Share-based compensation	1,132	710
Other operating activities, net	46,937	(6,057)
Net cash provided by operating activities	211,247	110,809
Cash flows from investing activities:
Purchase of property and equipment	(100,558)	(56,997)
Proceeds from sale of property and equipment	347	1,828
Net cash used in investing activities	(100,211)	(55,169)
Cash flows from financing activities:
Principal payments under long-term debt agreements	(50,000)	0
Proceeds From (Repayments Of) Line Of Credit	0	(9,975)
Payments for share repurchases	(17,299)	(50)
Dividends paid	(10,695)	(8,235)
Other financing activities, net	(567)	0
Net cash provided by (used in) financing activities	(78,561)	(18,260)
(Decrease) increase in cash and cash equivalents	32,475	37,380
Cash and cash equivalents at beginning of period	127,462	10,171
Cash and cash equivalents at end of period	$ 159,937	$ 47,551