Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
OPERATING ACTIVITIES
Net income	$ 14,377	$ 17,611
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	25,705	26,237
Deferred income taxes	(6,778)	(1,524)
Amortization of stock-based compensation	587	287
Gain on disposal of property and equipment	(1,288)	(10,181)
Changes in certain working capital items:
Trade receivables	2,512	3,290
Prepaid expenses and other current assets	1,666	1,475
Accounts payable, accrued liabilities, and accrued expenses	6,599	6,805
Accrued income taxes	12,530	11,690
Net cash provided by operating activities	55,910	55,690
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	3,783	25,547
Purchases of property and equipment, net of trades	(2,865)	(5,222)
Change in designated funds for equipment purchases	(3,875)	(18,205)
Change in other assets	(94)	1,658
Net cash (used in) provided by investing activities	(3,051)	3,778
FINANCING ACTIVITIES
Payments of Ordinary Dividends, Common Stock	(1,666)	0
Repayments on line of credit	0	(24,600)
Payments for Repurchase of Common Stock	(14,678)	0
Net cash used in financing activities	(16,344)	(24,600)
Net increase in cash and cash equivalents	36,515	34,868
CASH AND CASH EQUIVALENTS
Beginning of period	33,232	17,303
End of period	69,747	52,171
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest paid	0	40
Cash paid during the period for income taxes, net of refunds	221	492
Noncash investing and financing activities:
Purchased property and equipment in accounts payable	0	20,164
Sold property and equipment in other current assets	892	6,882
Common stock dividends declared in accounts payable	$ 0	$ 1,759