CONDENSED CONSOLIDATED BALANCE SHEET (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 27,932	$ 30,736
Accounts receivable, net	178,479	172,419
Income taxes receivable	1,972
Inventories	20,839	14,173
Derivative instruments	56,831	50,824
Other current assets	3,703	2,158
Total current assets	289,756	270,310
Properties and equipment, net (Successful efforts method)	4,690,176	4,310,977
Derivative instruments	8,708
Other assets	42,752	35,026
TOTAL ASSETS	5,031,392	4,616,313
Current liabilities
Accounts payable	335,349	312,480
Current portion of long-term debt		75,000
Accrued liabilities	59,234	49,789
Income taxes payable		1,667
Deferred income taxes	4,690	5,203
Total current liabilities	399,273	444,139
Postretirement benefits	41,041	38,864
Long-term debt	1,162,000	1,012,000
Deferred income taxes	986,943	882,672
Asset retirement obligation	70,525	67,016
Other liabilities	42,876	40,175
Total liabilities	2,702,658	2,484,866
Commitments and contingencies
Stockholders' equity
Common stock: Authorized -- 480,000,000 shares of $0.10 par value in 2013 and 2012, respectively Issued--421,959,520 shares and 420,859,462 shares in 2013 and 2012, respectively	42,196	42,086
Additional paid-in capital	698,383	695,566
Retained earnings	1,558,260	1,373,264
Accumulated other comprehensive income / (loss)	33,244	23,880
Less treasury stock, at cost: 808,800 shares in 2013 and 2012, respectively	(3,349)	(3,349)
Total stockholders' equity	2,328,734	2,131,447
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 5,031,392	$ 4,616,313