CONDENSED CONSOLIDATED BALANCE SHEET (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 47,277	$ 30,736
Accounts receivable, net	204,970	172,419
Income taxes receivable	7,273
Inventories	18,276	14,173
Deferred income taxes	50,864
Derivative instruments	69,644	50,824
Other current assets	4,889	2,158
Total current assets	403,193	270,310
Properties and equipment, net (Successful efforts method)	4,558,207	4,310,977
Derivative instruments	17,963
Other assets	38,573	35,026
TOTAL ASSETS	5,017,936	4,616,313
Current liabilities
Accounts payable	356,851	312,480
Current portion of long-term debt	75,000	75,000
Accrued liabilities	58,571	49,789
Income taxes payable	3,969	1,667
Deferred income taxes		5,203
Total current liabilities	494,391	444,139
Postretirement benefits	40,313	38,864
Long-term debt	1,067,000	1,012,000
Deferred income taxes	1,015,493	882,672
Asset retirement obligation	68,390	67,016
Other liabilities	46,108	40,175
Total liabilities	2,731,695	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--210,758,335 shares and 210,429,731 shares in 2013 and 2012, respectively	21,076	21,043
Additional paid-in capital	725,156	716,609
Retained earnings	1,496,795	1,373,264
Accumulated other comprehensive income / (loss)	46,563	23,880
Less treasury stock, at cost: 404,400 shares in 2013 and 2012, respectively	(3,349)	(3,349)
Total stockholders' equity	2,286,241	2,131,447
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 5,017,936	$ 4,616,313