Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012
Cash flows from operating activities:
Net income	$ 96,998		$ 189,812
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion, amortization and impairment	273,617		251,430
Provision for bad debts			1,600
Dry holes and abandonments	15		85
Deferred income tax expense	45,748		102,576
Stock-based compensation expense	12,119		11,240
Tax expense related to stock-based compensation			(1,208)
Net gain on asset disposals	(908)	[1]	(30,732)	[1]
Changes in operating assets and liabilities:
Accounts receivable	(36,025)		(10,448)
Income taxes receivable/payable	(8,480)		(4,458)
Inventory and other assets	(12,805)		6,108
Accounts payable	25,502		(8,466)
Accrued expenses	(12,453)		(11,262)
Other liabilities	15		(808)
Net cash provided by operating activities	383,343		495,469
Cash flows from investing activities:
Purchases of property and equipment	(332,598)		(512,065)
Proceeds from disposal of assets	4,593		58,945
Net cash used in investing activities	(328,005)		(453,120)
Cash flows from financing activities:
Purchases of treasury stock	(10,031)		(71,337)
Dividends paid	(14,673)		(15,438)
Tax benefit related to stock-based compensation	4,862
Proceeds from senior notes			300,000
Repayment of long-term debt	(2,500)		(92,500)
Proceeds from borrowing under revolving credit facility			123,400
Repayment of borrowing under revolving credit facility			(233,400)
Debt issuance costs			(1,549)
Proceeds from exercise of stock options	6,959		195
Net cash provided by (used in) financing activities	(15,383)		9,371
Effect of foreign exchange rate changes on cash	(1,801)		(367)
Net increase in cash and cash equivalents	38,154		51,353
Cash and cash equivalents at beginning of period	110,723		23,946
Cash and cash equivalents at end of period	148,877		75,299
Net cash paid during the period for:
Interest, net of capitalized interest of $4,358 in 2013 and $4,065 in 2012	(12,686)		(8,153)
Income taxes	(13,238)		(7,250)
Supplemental investing and financing information:
Net decrease in payables for purchases of property and equipment	(16,169)		(8,333)
Net decrease in deposits on equipment purchases	$ 13,789		$ 10,970

[1] Net gains or losses associated with the disposal of assets relate to corporate strategy decisions of the executive management group. Accordingly, the related gains or losses have been separately presented and excluded from the results of specific segments.