Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities:
Net income	$ 55,016	$ 51,991	$ 43,627
Noncash items included in net income:
Depreciation and amortization	65,020	59,022	51,564
Provision for doubtful accounts	1,463	1,942	2,227
Deferred income taxes	8,420	9,462	12,098
Loss (gain) from property disposals, net	310	(17)	(721)
Stock-based compensation	3,878	4,166	2,902
Changes in operating assets and liabilities:
Accounts receivable	6,896	(12,372)	(13,350)
Accounts payable	(382)	(8,590)	5,479
Other working capital items, net	(84)	(11,215)	(5,213)
Claims, insurance and other	(821)	5,260	392
Other, net	2,998	2,521	2,307
Net cash provided by operating activities	142,714	102,170	101,312
Investing Activities:
Acquisition of business, net of cash received	(22,238)
Acquisition of property and equipment	(86,499)	(97,750)	(126,358)
Proceeds from disposal of property and equipment	818	2,905	4,338
Net cash used in investing activities	(107,919)	(94,845)	(122,020)
Financing Activities:
Repayment of revolving credit agreement	(280,461)	(340,540)	(223,798)
Borrowing of revolving credit agreement	249,994	337,223	262,125
Proceeds from stock option exercises (including excess tax benefits)	2,533	7,623	4,948
Repayment of senior notes	(7,143)	(7,143)	(22,143)
Repayment of capital leases	(3,507)	(280)
Other financing activity	(454)		(586)
Net cash (used in) provided by financing activities	(39,038)	(3,117)	20,546
Net Increase (Decrease) in Cash and Cash Equivalents	(4,243)	4,208	(162)
Cash and cash equivalents, beginning of period	4,367	159	321
Cash and cash equivalents, end of period	124	4,367	$ 159
Non Cash Investing Activities
Equipment financed with capital leases	$ 27,054	$ 16,886