Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating Activities:
Net income	$ 79,601	$ 43,339
Noncash items included in net income:
Depreciation and amortization	74,965	64,607
Other, net	14,826	18,812
Changes in operating assets and liabilities, net	17,718	979
Net cash provided by operating activities	187,110	127,737
Investing Activities:
Acquisition of property and equipment	(155,217)	(155,676)
Proceeds from disposal of property and equipment	778	3,090
Net cash used in investing activities	(154,439)	(152,586)
Financing Activities:
Repayment of revolving credit agreement	(170,733)	(159,102)
Borrowing of revolving credit agreement	142,733	193,601
Proceeds from stock option exercises	4,165	2,531
Shares withheld for taxes	(1,396)	(1,249)
Repayment of senior notes		(3,571)
Repayment of capital leases	(11,631)	(8,819)
Net cash provided by (used in) financing activities	(36,862)	23,391
Net Decrease in Cash and Cash Equivalents	(4,191)	(1,458)
Cash and cash equivalents, beginning of period	4,720	1,539
Cash and cash equivalents, end of period	529	81
Non Cash Investing Activities
Equipment financed with capital leases	$ 28,052	$ 31,320