Derivatives - Fair Value Amounts of Derivatives and Placement in Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Prepaid and other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Cash collateral	$ 1,300	$ 2,700
Other long-term assets
Derivative Instruments, Gain (Loss) [Line Items]
Cash collateral	8,800	8,300
Commodity derivatives | Prepaid and other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	1,407	4,973
Commodity derivatives | Other accrued liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	(2,274)	(700)
J. Aron repurchase obligation derivative | Over the Counter | Obligations under Inventory Financing Agreements
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	(13,222)	4,085
MLC repurchase obligation derivative | Over the Counter | Obligations under Inventory Financing Agreements
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	(7,230)	0
Interest rate derivatives | Prepaid and other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	$ 0	$ 191