Derivatives - Fair Value Amounts of Derivatives and Placement in Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Prepaid and other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Cash collateral	$ 2,700	$ 2,700
Other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Cash collateral	9,500	8,300
Commodity derivatives | Prepaid and other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	1,730	4,973
Commodity derivatives | Other accrued liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	(16,878)	(700)
J. Aron repurchase obligation derivative | Over the Counter | Obligations under inventory financing agreements
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	165	4,085
MLC repurchase obligation derivative | Over the Counter | Obligations under inventory financing agreements
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	(5,639)	0
Interest rate derivatives | Prepaid and other current assets
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	0	191
Interest rate derivatives | Other accrued liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	(188)	0
Interest rate derivatives | Other liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Asset (Liability)	$ (1,286)	$ 0