Oil and Natural Gas Activities--Narrative (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Depreciation, depletion, and amortization expense of oil and natural gas properties	$ 179,734	$ 154,788	$ 132,307
Average depreciation, depletion and amortization rate per equivalent unit of production	18.45	16.98	15.29
Unproved property costs excluded from amortization	321,477	162,921
Incurred During Current Reporting Period
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Unproved property costs excluded from amortization	169,044
Incurred One Year Prior To Current Reporting Period
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Unproved property costs excluded from amortization	114,406
Incurred Two Years Prior To Current Reporting Period
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Unproved property costs excluded from amortization	9,372
Incurred More Than Two Years Prior To Current Reporting Period
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Unproved property costs excluded from amortization	$ 28,655
Minimum
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Evaluation period of oil and natural gas properties (in years)	2 years
Maximum
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Evaluation period of oil and natural gas properties (in years)	5 years