Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Apr. 23, 2014	Mar. 31, 2014		Dec. 31, 2013
Assets:
Proved oil and gas properties		$ 5,875,541		$ 5,637,462
Unproved oil and gas properties		287,607		271,100
Oil and gas properties held for sale net of accumulated depletion, depreciation and amortization of $31,776 in 2014 and $7,390 in 2013		42,276		19,072
Liabilities:
Line of Credit Facility, Amount Outstanding	0	0		0
Fair Value, Measurements, Nonrecurring [Member] | Level 1
Assets:
Proved oil and gas properties				0	[1]
Unproved oil and gas properties				0	[1]
Oil and gas properties held for sale net of accumulated depletion, depreciation and amortization of $31,776 in 2014 and $7,390 in 2013				0	[1]
Fair Value, Measurements, Nonrecurring [Member] | Level 2
Assets:
Proved oil and gas properties				0	[1]
Unproved oil and gas properties				0	[1]
Oil and gas properties held for sale net of accumulated depletion, depreciation and amortization of $31,776 in 2014 and $7,390 in 2013				0	[1]
Fair Value, Measurements, Nonrecurring [Member] | Level 3
Assets:
Proved oil and gas properties				62,178	[1]
Unproved oil and gas properties				3,280	[1]
Oil and gas properties held for sale net of accumulated depletion, depreciation and amortization of $31,776 in 2014 and $7,390 in 2013				650	[1]
Fair Value, Measurements, Recurring [Member] | Level 1
Liabilities:
Net Profits Plan Liability		0	[2]	0	[2]
Fair Value, Measurements, Recurring [Member] | Level 2
Liabilities:
Net Profits Plan Liability		0	[2]	0	[2]
Fair Value, Measurements, Recurring [Member] | Level 3
Liabilities:
Net Profits Plan Liability		55,209	[2]	56,985	[2]
Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member] | Level 1
Assets:
Derivatives		0	[2]	0	[2]
Liabilities:
Derivatives		0	[2]	0	[2]
Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member] | Level 2
Assets:
Derivatives		21,336	[2]	52,510	[2]
Liabilities:
Derivatives		68,569	[2]	31,020	[2]
Derivatives not designated as hedging instruments | Fair Value, Measurements, Recurring [Member] | Level 3
Assets:
Derivatives		0	[2]	0	[2]
Liabilities:
Derivatives		$ 0	[2]	$ 0	[2]

[1] This represents a non-financial asset or liability that is measured at fair value on a nonrecurring basis.

[2] This represents a financial asset or liability that is measured at fair value on a recurring basis.