Supplemental Financial Information (Parent - Cash Flow Statement) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Depletion and depreciation					$ 401,200,000	$ 292,951,000	$ 243,390,000
Ceiling test and other impairments	$ 3,144,899,000	$ 0	$ 0	$ 0	3,144,899,000	0	0
Deferred and current non-cash income taxes					(990,000)	995,000	(6,000)
Unrealized loss (gain) on commodity derivatives					104,190,000	(130,066,000)	25,876,000
Deferred gain on sale of liquids gathering system					(10,553,000)	(10,553,000)	(10,553,000)
(Gain) on sale of property					0	(8,022,000)	0
Excess tax benefit from stock based compensation					0	0	0
Stock compensation					4,128,000	5,467,000	9,767,000
Other					9,217,000	4,569,000	2,252,000
Net changes in operating assets and liabilities:
Restricted cash					2,000	2,000	2,000
Accounts receivable					65,132,000	(43,116,000)	16,565,000
Prepaid expenses and other					(20,106,000)	(1,920,000)	1,180,000
Other non-current assets					21,112,000	284,000	277,000
Accounts payable					13,815,000	28,696,000	(1,400,000)
Accrued liabilities					1,655,000	(5,938,000)	(32,904,000)
Production taxes payable					(3,312,000)	15,115,000	(7,207,000)
Interest payable					(3,441,000)	14,233,000	1,772,000
Other long-term obligations					(5,770,000)	6,427,000	3,296,000
Current taxes payable					1,580,000	609,000	(17,507,000)
Net cash provided by operating activities					515,538,000	712,584,000	472,638,000
Investing Activities:
Acquisition costs					3,964,000	(891,075,000)	(649,801,000)
Oil and gas property expenditures					(494,025,000)	(599,913,000)	(370,662,000)
Gathering system expenditures					0	(6,842,000)	(5,510,000)
Proceeds from sale of property					0	27,944,000	0
Proceeds from sale of liquids gathering system					0	0	(129,000)
Proceeds from sale of marketable securities					0	0	0
Change in capital cost accrual					(25,380,000)	(125,577,000)	(65,975,000)
Inventory					3,235,000	175,000	(627,000)
Purchase of property, plant and equipment					(551,000)	(5,455,000)	(815,000)
Net cash used in investing activities					(512,757,000)	(1,600,743,000)	(1,093,519,000)
Financing activities:
Borrowings on long-term debt					1,165,000,000	1,095,000,000	1,006,000,000
Payments on long-term debt					(1,153,000,000)	(1,037,000,000)	(823,000,000)
Proceeds from issuance of Senior Notes					0	850,000,000	450,000,000
Deferred financing costs					6,000	(13,245,000)	(8,958,000)
Repurchased shares/net share settlements					(2,514,000)	(9,111,000)	(5,429,000)
Shares re-issued from treasury					0	0	0
Excess tax benefit from stock based compensation					0	0	0
Payment of contingent consideration					(17,049,000)	0	0
Proceeds from exercise of options					0	770,000	11,000
Net cash provided by (used in) financing activities					(7,557,000)	886,414,000	618,624,000
(Decrease)/increase in cash during the period					(4,776,000)	(1,745,000)	(2,257,000)
Cash and cash equivalents, beginning of period				8,919,000	8,919,000	10,664,000	12,921,000
Cash and cash equivalents, end of period	4,143,000				4,143,000	8,919,000	10,664,000
Cash paid for:
Interest					169,867,000	108,889,000	99,542,000
Income taxes					0	1,752,000	13,843,000
Non Cash Investing Activities Oil And Gas Properties					0	20,000,000	12,651,000
Parent [Member]
Net changes in operating assets and liabilities:
Net cash provided by operating activities					(101,277,000)	(35,818,000)	17,772,000
Investing Activities:
Investment in subsidiary					0	(850,000,000)	(464,405,000)
Dividends received					96,297,000	52,741,000	4,580,000
Net cash used in investing activities					96,297,000	(797,259,000)	(459,825,000)
Financing activities:
Proceeds from issuance of Senior Notes					0	850,000,000	450,000,000
Deferred financing costs					6,000	(13,245,000)	(8,958,000)
Repurchased shares/net share settlements					0	(6,471,000)	(3,311,000)
Shares re-issued from treasury					4,725,000	2,936,000	1,496,000
Net cash provided by (used in) financing activities					4,731,000	833,220,000	439,227,000
(Decrease)/increase in cash during the period					(249,000)	143,000	(2,826,000)
Cash and cash equivalents, beginning of period				$ 772,000	772,000	629,000	3,455,000
Cash and cash equivalents, end of period	$ 523,000				$ 523,000	$ 772,000	$ 629,000