Inventory Financing Agreements - Supply and Offtake Agreements (Details) $ in Thousands			3 Months Ended
	Dec. 05, 2018 USD ($) mbpd	Jun. 27, 2018	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Feb. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 01, 2018 USD ($)	Jun. 01, 2015 USD ($)
Supply Commitment [Line Items]
Supply and exchange agreement expenses			$ 18,674	$ 18,710
Supply and Offtake Agreements
Supply Commitment [Line Items]
Agreement extension term			1 year
Deferred payment arrangement, aggregate marginal increase	$ 2,500
Barrels of crude per day provided (up to) (in mbpd) | mbpd	150
Supply and exchange agreement expenses			$ 1,300	1,700
Amount of deferred payment arrangement	$ 165,000
Percentage of receivables and inventory for deferred payment arrangement		85.00%
Deferral arrangement fee								$ 1,300
Capacity of deferred payment arrangement			104,800			$ 155,500
Outstanding amount of deferred payment arrangement			79,300			97,500
Fee agreement receivable (payable)			1,400		$ 800	$ 500	$ 2,200
Supply and Offtake Agreements | London Interbank Offered Rate (LIBOR)
Supply Commitment [Line Items]
Margin on LIBOR rate	3.50%
Deferred payment availability fee	0.75%
Supply and Offtake Agreements | Inventory Intermediation
Supply Commitment [Line Items]
Handling fees			$ 6,900	$ 5,400