Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
OPERATING ACTIVITIES
Net income	$ 36,568	$ 43,272
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	74,379	78,823
Deferred income taxes	3,165	(5,679)
Stock-based compensation	340	0
Amortization of stock-based compensation, net of tax	0	740
Gain on disposal of property and equipment	(19,845)	(7,273)
Changes in certain working capital items:
Trade receivables	8,778	9,305
Prepaid expenses and other current assets	(5,914)	2,191
Accounts payable, accrued liabilities, and accrued expenses	(13,221)	1,291
Accrued income taxes	(7,035)	(2,474)
Net cash provided by operating activities	77,215	120,196
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	78,046	37,306
Purchases of property and equipment, net of trades	(104,883)	(69,979)
Change in designated funds for equipment purchases	3,866	(824)
Change in designated funds for claims acquired	(14,774)	0
Acquisition of business, net of cash acquired	(87,635)	0
Change in other assets	(550)	10
Net cash used in investing activities	(125,930)	(33,487)
FINANCING ACTIVITIES
Payments of cash dividends	(5,000)	(4,999)
Shares withheld for employee taxes related to stock-based compensation	(198)	0
Repurchases of common stock	0	(14,678)
Pay down of debt	(23,303)	0
Net cash used in financing activities	(28,501)	(19,677)
Net (decrease) increase in cash and cash equivalents	(77,216)	67,032
CASH AND CASH EQUIVALENTS
Beginning of period	128,507	33,232
End of period	51,291	100,264
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid during the period for income taxes, net of refunds	21,753	29,779
Noncash investing and financing activities:
Purchased property and equipment in accounts payable	$ 7,000	$ 2,527