Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash Flows from Operating Activities:
Net Income	$ 7,209	$ 3,570
Adjustments to reconcile net income to net cash provided by operation activities -
Depreciation, depletion, and amortization	60,120	61,363
Accretion of asset retirement obligation	1,775	1,112
Deferred income taxes	4,377	2,312
Stock-based compensation expenses	3,015	3,629
Other	(3,864)	(2,889)
Decrease in accounts receivable	(5,191)	3,193
Increase (decrease) in accounts payable and accrued liabilities	3,085	(7,913)
Increase (decrease) in accrued interest	(8,303)	(594)
Net Cash Provided by Operating Activities	62,223	63,783
Cash Flows from Investing Activities:
Additions to property and equipment	(132,981)	(187,915)
Proceeds from the sale of property and equipment	999	532
Net Cash Used in Investing Activities	(131,982)	(187,383)
Cash Flows from Financing Activities:
Proceeds from Lines of Credit	70,300	0
Net proceeds from issuances of common stock	946	1,329
Purchase of treasury shares	(1,409)	(2,636)
Net Cash Used in Financing Activities	69,837	(1,307)
Net Decrease in Cash and Cash Equivalents	78	(124,907)
Cash and Cash Equivalents at Beginning of Period	170	251,696
Cash and Cash Equivalents at End of Period	248	126,789
Supplemental Disclosures of Cash Flows Information:
Cash paid during period for interest, net of amounts capitalized	$ 24,626	$ 13,415