Condensed Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net income	$ 164,210	$ 141,673
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	100,736	91,252
(Gain) loss on sale of property and equipment	485	466
Share-based compensation	1,590	480
Other operating activities, net	(28,507)	58,360
Net cash provided by operating activities	238,514	292,231
Cash flows from investing activities:
Purchase of property and equipment	(188,318)	(295,533)
Proceeds from sale of property and equipment	7,389	2,997
Net cash used in investing activities	(180,929)	(292,536)
Cash flows from financing activities:
Principal payments under long-term debt agreements	0	(26,488)
Proceeds From (Repayments Of) Line Of Credit	(9,975)	111,015
Payments for share repurchases	(7,135)	(84,683)
Dividends paid	(16,469)	0
Other financing activities, net	(344)	(338)
Net cash provided by (used in) financing activities	(33,923)	(494)
(Decrease) increase in cash and cash equivalents	23,662	(799)
Cash and cash equivalents at beginning of period	10,171	11,472
Cash and cash equivalents at end of period	$ 33,833	$ 10,673