Quarterly report pursuant to Section 13 or 15(d)

Acquisitions (Details)

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Acquisitions (Details) (USD $)
1 Months Ended 9 Months Ended 0 Months Ended
Feb. 28, 2011
Sep. 30, 2013
Sep. 30, 2012
May 31, 2013
Feb. 15, 2013
Common Stock [Member]
Public Offering [Member]
Jan. 07, 2013
Common Stock [Member]
Public Offering [Member]
Dec. 24, 2012
Common Stock [Member]
Public Offering [Member]
Feb. 15, 2013
Utica Shale [Member]
well
acre
Dec. 21, 2012
Utica Shale [Member]
Dec. 18, 2012
Utica Shale [Member]
Dec. 19, 2012
Utica Shale [Member]
acre
Dec. 24, 2012
Utica Shale [Member]
acre
Dec. 17, 2012
Utica Shale [Member]
acre
Business Acquisition [Line Items]                          
Period allowed for refusal 6 months                        
Affiliates participation ratio 50.00%                        
Gas and oil acreage, undeveloped, net               22,000     7,000 37,000 30,000
Cash price of ownership interest               $ 220,000,000 $ 70,000,000 $ 302,000,000 $ 372,000,000    
Amount put in escrow       (10,000,000)       33,600,000     53,900,000    
Stock option, portion attributable to underwriters (shares)           900,000 750,000            
Proceeds from issuance of common stock, net of offering costs   $ 359,040,000      $ 325,800,000   $ 460,700,000 $ 325,800,000       $ 460,700,000  
Increase in lease interest, percentage               16.20%          
Lease interest, percentage               93.80%          
Existing wells excluded               14          
Future wells excluded               16