CONSOLIDATED STATEMENT OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING REVENUES
Natural gas	$ 1,025,044	$ 1,590,625	$ 1,405,262
Crude oil and condensate	248,211	313,889	291,418
Gain (loss) on derivative instruments	56,686	219,319	0
Brokered natural gas	16,383	34,416	36,450
Other	10,826	14,762	13,148
TOTAL OPERATING REVENUES	1,357,150	2,173,011	1,746,278
OPERATING EXPENSES
Direct operations	140,814	145,529	140,856
Transportation and gathering	427,588	349,321	229,489
Brokered natural gas	12,592	30,030	29,936
Taxes other than income	42,809	47,012	43,045
Exploration	27,460	28,746	18,165
Depreciation, depletion and amortization	622,211	632,760	651,052
Impairment of oil and gas properties	114,875	771,037	0
General and administrative	69,444	82,590	104,606
TOTAL OPERATING EXPENSES	1,457,793	2,087,025	1,217,149
Earnings (loss) on equity method investments	6,415	3,080	1,102
Gain (loss) on sale of assets	3,866	17,120	21,351
INCOME (LOSS) FROM OPERATIONS	(90,362)	106,186	551,582
Interest expense	96,911	73,785	66,044
Income (loss) before income taxes	(187,273)	32,401	485,538
Income tax expense (benefit)	(73,382)	(72,067)	205,765
NET INCOME (LOSS)	$ (113,891)	$ 104,468	$ 279,773
Earnings (loss) per share
Basic (in dollars per share)	$ (0.28)	$ 0.25	$ 0.67
Diluted (in dollars per share)	$ (0.28)	$ 0.25	$ 0.66
Weighted-average common shares outstanding
Basic (in shares)	413,696	415,840	420,188
Diluted (in shares)	413,696	417,601	422,375
Dividends per common share (in dollars per share)	$ 0.08	$ 0.08	$ 0.06