Fair Value Recurring Measurements (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Swaps | Commodity Contracts
Assets:
Derivative Assets	$ 7,655	$ 14,799
Swaps | Interest Rate Swaps
Liabilities:
Derivative Liabilities	3,399	2,176
Forward Contracts | Commodity Contracts
Liabilities:
Derivative Liabilities	918	592
Forward Contracts | Fair Value Hedges
Assets:
Derivative Assets	21,456	33,797
Level 1 | Swaps | Commodity Contracts
Assets:
Derivative Assets	0	0
Level 1 | Swaps | Interest Rate Swaps
Liabilities:
Derivative Liabilities	0	0
Level 1 | Forward Contracts | Commodity Contracts
Liabilities:
Derivative Liabilities	918	592
Level 1 | Forward Contracts | Fair Value Hedges
Assets:
Derivative Assets	0	0
Level 2 | Swaps | Commodity Contracts
Assets:
Derivative Assets	7,655	14,799
Level 2 | Swaps | Interest Rate Swaps
Liabilities:
Derivative Liabilities	3,399	2,176
Level 2 | Forward Contracts | Commodity Contracts
Liabilities:
Derivative Liabilities	0	0
Level 2 | Forward Contracts | Fair Value Hedges
Assets:
Derivative Assets	21,456	33,797
Level 3 | Swaps | Commodity Contracts
Assets:
Derivative Assets	0	0
Level 3 | Swaps | Interest Rate Swaps
Liabilities:
Derivative Liabilities	0	0
Level 3 | Forward Contracts | Commodity Contracts
Liabilities:
Derivative Liabilities	0	0
Level 3 | Forward Contracts | Fair Value Hedges
Assets:
Derivative Assets	$ 0	$ 0