Consolidated Statements of Cash Flows (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
OPERATING ACTIVITIES
Net income	$ 37,412	$ 28,540
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	26,360	31,102
Deferred income taxes	9,533	(6,510)
Gain on disposal of property and equipment	(15,530)	(2,533)
Changes in certain working capital items:
Trade receivables	(5,268)	(5,231)
Prepaid expenses and other current assets	(9,508)	(1,153)
Accounts payable, accrued liabilities, and accrued expenses	1,850	5,386
Accrued income taxes	(3,070)	(1,666)
Net cash provided by operating activities	41,779	47,935
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	30,893	9,429
Purchases of property and equipment, net of trades	(60,742)	(160)
Maturity and calls of investments	21,650	26,450
Purchases of investments	0	(17,409)
Change in other assets	(1,469)	(512)
Net cash provided by (used in) investing activities	(9,668)	17,798
FINANCING ACTIVITIES
Cash dividend	$ (1,814)	$ (1,813)
Net cash used in financing activities	(1,814)	(1,813)
Net increase in cash and cash equivalents	30,297	63,920
Beginning of period	121,120	52,351
End of period	151,417	116,271
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid during the period for income taxes, net of refunds	11,131	18,320
Noncash investing and financing activities:
Purchased property and equipment in accounts payable	4,738	88
Common stock dividends declared in accounts payable	$ 1,814	$ 1,814