Acquisitions (Details)									1 Months Ended		3 Months Ended								12 Months Ended			21 Months Ended
	Aug. 31, 2015 USD ($)	Jun. 29, 2015 USD ($) a	Jun. 12, 2015 USD ($) a well mi MMcf	Jun. 09, 2015 USD ($) a	Apr. 21, 2015 USD ($)	Mar. 20, 2014 USD ($)	Nov. 13, 2013 USD ($)	Feb. 15, 2013 USD ($)	Apr. 30, 2015 USD ($) a	Feb. 28, 2011	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($)	Feb. 28, 2014 a
Business Acquisition [Line Items]
Proceeds from issuance of common stock, net of offering costs and exercise of stock options			$ 479,700,000		$ 501,800,000														$ 981,568,000	$ 689,000	$ 766,495,000
Revenues											$ 190,319,000	$ 230,569,000	$ 112,270,000	$ 176,317,000	$ 267,697,000	$ 170,804,000	$ 114,736,000	$ 118,029,000	709,475,000	671,266,000	262,753,000
Lease operating expenses																			69,475,000	52,191,000	26,703,000
Period allowed for refusal										6 months
Affiliates participation ratio										50.00%
Gas And Oil Area, Gross | a		4,950
Deductions to cash held in escrow																			8,000	$ 8,000	$ 8,000
Common Stock | Public Offering
Business Acquisition [Line Items]
Proceeds from issuance of common stock, net of offering costs and exercise of stock options							$ 408,000,000	$ 325,800,000
Utica Shale
Business Acquisition [Line Items]
Gas and oil acreage, undeveloped, net | a																							8,000
Purchase price																			182,000,000
Cash, net of purchase price adjustments						$ 179,527,000													179,500,000
Revenues																						$ 6,400,000
Lease operating expenses																						$ 1,000,000
Goodwill, Acquired During Period																			0
Paloma Partners III, LLC
Business Acquisition [Line Items]
Amount put in escrow	$ 30,100,000								$ 75,000,000
Purchase price	$ 302,300,000								$ 301,900,000
Gas And Oil Area, Net | a									24,000
American Energy - Utica, LLC
Business Acquisition [Line Items]
Amount put in escrow				$ 67,100,000
Purchase price		$ 405,400,000
Cash, net of purchase price adjustments		405,000,000	$ 405,029,000
Deductions to cash held in escrow																			$ 2,400,000
Goodwill, Acquired During Period				$ 0
Belmont And Jefferson Counties, Ohio
Business Acquisition [Line Items]
Gas And Oil Area, Gross And Net | a				6,198
Purchase price				$ 68,200,000
Monroe County, Ohio
Business Acquisition [Line Items]
Gas And Oil Area, Net | a			27,228
Gas And Oil Area, Gross | a			38,965
Monroe County, Ohio | American Energy - Utica, LLC
Business Acquisition [Line Items]
Purchase price		$ 18,200,000	$ 319,000,000
Gas And Oil Area, Net | a		1,900
Oil And Gas Delivery Commitments And Contracts, Daily Production, Volume | MMcf			14.6
Productive Oil And Gas Wells, Number Of Wells, Gross | well			18
Productive Oil And Gas Wells, Number Of Wells, Net | well			11.3
Gas Gathering, Transportation, Length | mi			11
Number Of Locations For Productive Wells | well			4