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v3.3.1.900

Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Aug. 18, 2014 | Apr. 23, 2014 | Dec. 21, 2012 | Oct. 17, 2012
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Asset retirement obligation capitalized |  | $ 8,800 | $ 9,295 | $ 3,556 |  |  |  |
Unamortized discount |  | 2,500 |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net | [1] | (12,493) | $ (14,658) |  |  |  |  |
Fair value of notes |  | 846,900 |  |  |  |  |  |
December Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Unamortized premium |  | 300 |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  | 1,100 |  |  |  |  |  |
August Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Unamortized premium |  | 14,700 |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  | 4,900 |  |  |  |  |  |
October Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  | 5,100 |  |  |  |  |  |
April Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Unamortized Discount (Premium), Net |  |  |  |  |  | $ 6,800 |  |
Senior Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Carrying value of debt |  | 944,600 |  |  |  |  |  |
Unamortized discount |  |  |  |  |  |  |  | $ 3,700
Unamortized premium |  |  |  |  | $ 18,000 |  | $ 500 |
Level 3 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Asset retirement obligation capitalized |  | $ 8,800 |  |  |  |  |  |
[1] | The October Notes were issued at a price of 98.534% resulting in a gross discount of $3.7 million and an effective rate of 8.000%. The December Notes were issued at a price of 101.000% resulting in a gross premium of $0.5 million and an effective rate of 7.531%. The August Notes were issued at a price of 106.000% resulting in a gross premium of $18.0 million and an effective rate of 6.561%. The April Notes were issued at par. The premium and discount are being amortized using the effective interest method.

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