Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
OPERATING ACTIVITIES
Net income	$ 43,272	$ 56,041
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	78,823	82,053
Deferred income taxes	(5,679)	(4,569)
Amortization of stock-based compensation, net of tax	740	1,042
Gain on disposal of property and equipment	(7,273)	(27,250)
Changes in certain working capital items:
Trade receivables	9,305	12,515
Prepaid expenses and other current assets	2,191	3,337
Accounts payable, accrued liabilities, and accrued expenses	1,291	7,001
Accrued income taxes	(2,474)	12,777
Net cash provided by operating activities	120,196	142,947
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	37,306	89,073
Purchases of property and equipment, net of trades	(69,979)	(111,688)
Change in designated funds for equipment purchases	(824)	(12,488)
Change in other assets	10	1,495
Net cash used in investing activities	(33,487)	(33,608)
FINANCING ACTIVITIES
Payments of Ordinary Dividends, Common Stock	(4,999)	(5,254)
Contingent consideration related to acquisition	0	(1,765)
Repayments on line of credit	0	(24,600)
Repurchases of common stock	(14,678)	(30,858)
Net cash used in financing activities	(19,677)	(62,477)
Net increase in cash and cash equivalents	67,032	46,862
CASH AND CASH EQUIVALENTS
Beginning of period	33,232	17,303
End of period	100,264	64,165
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest paid	0	40
Cash paid during the period for income taxes, net of refunds	29,779	24,562
Noncash investing and financing activities:
Purchased property and equipment in accounts payable	2,527	10,956
Sold property and equipment in other current assets	1,803	12,488
Treasury stock acquired in accounts payable	$ 0	$ 4,911