Inventory Financing Agreements - Supply and Offtake Agreements (Details)		3 Months Ended		9 Months Ended
	Dec. 05, 2018 USD ($) mbpd	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jun. 01, 2018 USD ($)	Dec. 01, 2016 USD ($) installment	Jun. 01, 2015 USD ($)
Supply Commitment [Line Items]
Supply and exchange agreement expenses		$ 18,348,000	$ 10,425,000	$ 57,336,000	$ 29,346,000
Supply and Offtake Agreements
Supply Commitment [Line Items]
Agreement extension term				1 year
Deferred payment arrangement, aggregate marginal increase	$ 2,500,000
Barrels of crude per day provided (up to) | mbpd	150
Supply and exchange agreement expenses		1,300,000	1,300,000	$ 4,300,000	3,300,000
Amount of deferred payment arrangement	$ 165,000,000
Percentage of receivables and inventory for deferred payment arrangement	85.00%
Deferral arrangement fee									$ 1,300,000
Capacity of deferred payment arrangement		101,000,000.0		101,000,000.0		$ 77,400,000
Outstanding amount of deferred payment arrangement		94,800,000		94,800,000		68,400,000
Number of fee agreement payments | installment								18
Fee agreement receivable (payable)		(100,000)		(100,000)		$ 2,500,000	$ 2,200,000	$ 14,600,000
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		$ 9,100,000	$ 5,000,000.0	$ 24,700,000	$ 15,800,000