Derivative Instruments (Commodity Derivative Instruments by Type Table) (Details) $ in Thousands	Dec. 31, 2016 USD ($) MMBTU bbl $ / MMBTU $ / bbl
Derivatives Fair Value [Line Items]
Fair Value Liability	$ (49,414)
Natural Gas - Fixed Price Swaps
Derivatives Fair Value [Line Items]
Fair Value Liability	(32,658)
Crude Oil - Fixed Price Swaps
Derivatives Fair Value [Line Items]
Fair Value Liability	$ (16,756)
Designated as Hedging Instrument | Natural Gas - Fixed Price Swaps Production Period Ending December 31, 2017
Derivatives Fair Value [Line Items]
Derivatives Nonmonetary Volume Notional Amount | MMBTU	51,679,700	[1]
Derivative, Swap Type, Average Fixed Price | $ / MMBTU	3.140	[1]
Fair Value Liability	$ (24,579)	[2]
Designated as Hedging Instrument | Natural Gas - Fixed Price Swaps Production Period Ending December 31, 2018
Derivatives Fair Value [Line Items]
Derivatives Nonmonetary Volume Notional Amount | MMBTU	47,559,300	[1]
Derivative, Swap Type, Average Fixed Price | $ / MMBTU	2.959	[1]
Fair Value Liability	$ (8,079)	[2]
Designated as Hedging Instrument | Crude Oil - Fixed Price Swaps Production Period Ending December 31, 2017
Derivatives Fair Value [Line Items]
Derivatives Nonmonetary Volume Notional Amount | bbl	1,188,700	[1]
Derivative, Swap Type, Average Fixed Price | $ / bbl	46.971	[1]
Fair Value Liability	$ (10,220)	[2]
Designated as Hedging Instrument | Crude Oil - Fixed Price Swaps Production Period Ending December 31, 2018
Derivatives Fair Value [Line Items]
Derivatives Nonmonetary Volume Notional Amount | bbl	1,011,100	[1]
Derivative, Swap Type, Average Fixed Price | $ / bbl	49.544	[1]
Fair Value Liability	$ (6,536)	[2]

[1] Volumes for natural gas are stated in million British Thermal Units. Volumes for crude oil are stated in barrels.

[2] Fair value for natural gas fixed price swaps are based on forward NYMEX natural gas prices, as applicable. Fair value of crude oil fixed price swaps are based on forward West Texas Intermediate (“WTI”) index crude oil prices, as applicable.