Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 171,418		$ 240,618
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion, amortization and impairment	414,351		393,823
Provision for bad debts			1,600
Dry holes and abandonments	54		117
Deferred income tax expense	63,133		131,731
Stock-based compensation expense	19,028		17,203
Tax expense related to stock-based compensation			(1,206)
Net gain on asset disposals	(2,286)	[1]	(32,695)	[1]
Changes in operating assets and liabilities:
Accounts receivable	(23,662)		47,489
Income taxes receivable/payable	(5,586)		(3,315)
Inventory and other assets	3,090		8,857
Accounts payable	22,207		(13,102)
Accrued expenses	(4,895)		(8,030)
Other liabilities	(152)		(740)
Net cash provided by operating activities	656,700		782,350
Cash flows from investing activities:
Purchases of property and equipment	(483,284)		(744,348)
Proceeds from disposal of assets	8,282		63,695
Net cash used in investing activities	(475,002)		(680,653)
Cash flows from financing activities:
Purchases of treasury stock	(73,406)		(110,186)
Dividends paid	(21,904)		(22,956)
Tax benefit related to stock-based compensation	4,791
Proceeds from senior notes			300,000
Repayment of long-term debt	(3,750)		(92,500)
Proceeds from borrowing under revolving credit facility			123,400
Repayment of borrowing under revolving credit facility			(233,400)
Debt issuance costs			(7,531)
Proceeds from exercise of stock options	6,959		260
Net cash used in financing activities	(87,310)		(42,913)
Effect of foreign exchange rate changes on cash	(475)		743
Net increase in cash and cash equivalents	93,913		59,527
Cash and cash equivalents at beginning of period	110,723		23,946
Cash and cash equivalents at end of period	204,636		83,473
Net cash paid during the period for:
Interest, net of capitalized interest of $6,016 in 2013 and $6,391 in 2012	(12,703)		(7,408)
Income taxes	(31,361)		(8,120)
Supplemental investing and financing information:
Net decrease in payables for purchases of property and equipment	(29,818)		(13,288)
Net decrease in deposits on equipment purchases	$ 2,749		$ 44,762

[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.