Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Activities:
Net income	$ 21,125	$ 11,395
Noncash items included in net income:
Depreciation and amortization	23,030	20,087
Other, net	3,608	5,411
Changes in operating assets and liabilities, net	(12,261)	(12,765)
Net cash provided by operating activities	35,502	24,128
Investing Activities:
Acquisition of property and equipment	(46,881)	(88,388)
Proceeds from disposal of property and equipment	100	607
Net cash used in investing activities	(46,781)	(87,781)
Financing Activities:
Repayment of revolving credit agreement	(42,718)	(15,441)
Borrowing of revolving credit agreement	50,550	80,624
Proceeds from stock option exercises	4,018	1,288
Shares withheld for taxes	(1,302)	(1,211)
Repayment of capital leases	(3,493)	(2,435)
Net cash provided by financing activities	7,055	62,825
Net Decrease in Cash and Cash Equivalents	(4,224)	(828)
Cash and cash equivalents, beginning of period	4,720	1,539
Cash and cash equivalents, end of period	496	711
Non Cash Investing Activities
Equipment financed with capital leases	$ 5,318	$ 20,369