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Subsequent Events (Details) (USD $)
In Thousands, except Share data, unless otherwise specified |
0 Months Ended | 3 Months Ended | 12 Months Ended | 0 Months Ended | 0 Months Ended | 1 Months Ended | 0 Months Ended | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Dec. 24, 2012
|
Mar. 31, 2013
|
Mar. 31, 2012
|
Dec. 31, 2012
|
Dec. 31, 2011
|
Dec. 31, 2010
|
Feb. 15, 2013
Utica Shale [Member]
well
acre
|
Dec. 24, 2012
Utica Shale [Member]
acre
|
Dec. 31, 2012
Utica Shale [Member]
acre
|
Dec. 21, 2012
Utica Shale [Member]
acre
|
Dec. 19, 2012
Utica Shale [Member]
acre
|
Dec. 17, 2012
Utica Shale [Member]
acre
|
Feb. 15, 2013
Subsequent Event [Member]
Utica Shale [Member]
well
acre
|
Feb. 28, 2013
Subsequent Event [Member]
Utica Shale [Member]
|
Jan. 07, 2013
Subsequent Event [Member]
Utica Shale [Member]
acre
|
Dec. 31, 2012
Subsequent Event [Member]
Utica Shale [Member]
|
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]
|
Jan. 07, 2013
Common Stock [Member]
Public Offering [Member]
|
Dec. 05, 2011
Common Stock [Member]
Public Offering [Member]
|
Jul. 15, 2011
Common Stock [Member]
Public Offering [Member]
|
Mar. 30, 2011
Common Stock [Member]
Public Offering [Member]
|
May 25, 2010
Common Stock [Member]
Public Offering [Member]
|
May 25, 2010
Common Stock [Member]
Public Offering [Member]
|
May 19, 2010
Common Stock [Member]
Public Offering [Member]
|
Feb. 15, 2013
Common Stock [Member]
Public Offering [Member]
Subsequent Event [Member]
|
Jan. 07, 2013
Common Stock [Member]
Public Offering [Member]
Subsequent Event [Member]
|
Jan. 07, 2013
Common Stock [Member]
Public Offering [Member]
Subsequent Event [Member]
|
|
| Subsequent Event [Line Items] | |||||||||||||||||||||||||||||
| Issuance of common stock in public offering, shares | 8,912,500 | 11,750,000 | 4,600,000 | 3,450,000 | 2,760,000 | 1,481,481 | 8,912,500 | ||||||||||||||||||||||
| Stock option, portion attributable to underwriters (shares) | 900,000 | 750,000 | 187,022 | ||||||||||||||||||||||||||
| Stock option, portion available to underwriters (shares) | 1,650,000 | 900,000 | |||||||||||||||||||||||||||
| Proceeds from issuance of common stock | $ 427,900 | $ 357,640 | $ 427,091 | $ 307,154 | $ 21,879 | $ 325,800 | $ 460,700 | $ 325,800 | $ 427,900 | $ 460,700 | $ 128,000 | $ 94,700 | $ 84,300 | $ 21,600 | $ 325,800 | $ 460,700 | |||||||||||||
| Share price (usd per share) | $ 38.00 | $ 38.00 | $ 29.00 | $ 28.75 | $ 32.00 | $ 13.50 | $ 38.00 | ||||||||||||||||||||||
| Gas and oil areage, undeveloped, net | 22,000 | 37,000 | 106,000 | 37,000 | 7,000 | 30,000 | 22,000 | 37,000 | |||||||||||||||||||||
| Cash price of ownership interest | $ 320,489 | $ 84,778 | $ 757,192 | $ 287,292 | $ 101,644 | $ 220,000 | |||||||||||||||||||||||
| Number of wells excluded from acquisition | 14 | ||||||||||||||||||||||||||||
| Number of proposed future wells excluded from acquisition | 16 | 16 | |||||||||||||||||||||||||||
| Ownership percentage of acreage | 93.80% | 77.70% | |||||||||||||||||||||||||||
| Ownership percentage, additional acreage purchased | 16.20% | ||||||||||||||||||||||||||||