Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating Activities:
Net income	$ 28,990	$ 23,850
Noncash items included in net income:
Depreciation and amortization	42,269	36,983
Other, net	14,380	6,351
Changes in operating assets and liabilities, net	(6,322)	(720)
Net cash provided by operating activities	79,317	66,464
Investing Activities:
Acquisition of property and equipment	(127,330)	(102,140)
Proceeds from disposal of property and equipment	923	595
Net cash used in investing activities	(126,407)	(101,545)
Financing Activities:
Repayment of revolving credit agreement	(70,386)	(73,372)
Borrowing of revolving credit agreement	125,400	116,128
Proceeds from stock option exercises	1,288	248
Shares withheld for taxes	(1,211)	(650)
Repayment of senior notes	(3,571)	(3,572)
Repayment of capital leases	(5,570)	(3,465)
Net cash provided by financing activities	45,950	35,317
Net Increase (Decrease) in Cash and Cash Equivalents	(1,140)	236
Cash and cash equivalents, beginning of period	1,539	124
Cash and cash equivalents, end of period	399	360
Non Cash Investing Activities
Equipment financed with capital leases	$ 28,691	$ 34,683