Derivatives - Fair Value Amounts of Derivatives and Placement in Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Prepaid and other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Cash collateral	$ 700	$ 2,700
Other long-term assets
Derivative Instruments, Gain (Loss) [Line Items]
Cash collateral	7,000	7,000
Commodity derivatives | Prepaid and other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	1,561	0
Commodity derivatives | Other long-term assets
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	571	2,748
Commodity derivatives | Other accrued liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	(58)	(595)
J. Aron repurchase obligation derivative | Over the Counter
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	(24,995)	(20,000)
Interest rate derivatives | Prepaid and other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	851	161
Interest rate derivatives | Other long-term assets
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	2,115	3,377
Interest rate derivatives | Other accrued liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	$ 0	$ (94)