CONSOLIDATED STATEMENT OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING REVENUES
Natural gas	$ 1,506,078	$ 1,022,590	$ 1,025,044
Crude oil and condensate	212,338	151,106	248,211
Gain (loss) on derivative instruments	16,926	(38,950)	56,686
Brokered natural gas	17,217	13,569	16,383
Other	11,660	7,362	10,826
TOTAL OPERATING REVENUES	1,764,219	1,155,677	1,357,150
OPERATING EXPENSES
Direct operations	102,310	100,696	140,814
Transportation and gathering	481,439	436,542	427,588
Brokered natural gas	15,252	10,785	12,592
Taxes other than income	33,487	29,223	42,809
Exploration	21,526	27,662	27,460
Depreciation, depletion and amortization	568,817	590,128	622,211
Impairment of oil and gas properties and other assets	482,811	435,619	114,875
General and administrative	97,786	85,633	67,996
TOTAL OPERATING EXPENSES	1,803,428	1,716,288	1,456,345
Earnings (loss) on equity method investments	(100,486)	(2,477)	6,415
Gain (loss) on sale of assets	(11,565)	(1,857)	3,866
LOSS FROM OPERATIONS	(151,260)	(564,945)	(88,914)
Interest expense, net	82,130	88,336	96,911
Loss on debt extinguishment	0	4,709	0
Other expense (income)	(4,955)	1,609	1,448
Loss before income taxes	(228,435)	(659,599)	(187,273)
Income tax benefit	(328,828)	(242,475)	(73,382)
NET INCOME (LOSS)	$ 100,393	$ (417,124)	$ (113,891)
Earnings (loss) per share
Basic (in dollars per share)	$ 0.22	$ (0.91)	$ (0.28)
Diluted (in dollars per share)	$ 0.22	$ (0.91)	$ (0.28)
Weighted-average common shares outstanding
Basic (in shares)	463,735	456,847	413,696
Diluted (in shares)	465,551	456,847	413,696
Dividends per common share (in dollars per share)	$ 0.17	$ 0.08	$ 0.08