Derivatives - Narrative (Details) bbl in Thousands	3 Months Ended
	Mar. 31, 2019 bbl
Credit Derivatives [Line Items]
Derivative contracts, barrels	(212)
5.00% Convertible Senior Notes due 2021
Credit Derivatives [Line Items]
Debt instrument, interest rate	5.00%
5.00% Convertible Senior Notes due 2021 | Convertible Debt
Credit Derivatives [Line Items]
Debt instrument, interest rate	5.00%
Future
Credit Derivatives [Line Items]
Derivative contracts, barrels	(128)
Swap [Member]
Credit Derivatives [Line Items]
Derivative contracts, barrels	(340)
Long
Credit Derivatives [Line Items]
Derivative contracts, barrels	(7,041)
Long | Future
Credit Derivatives [Line Items]
Derivative contracts, barrels	(381)
Long | Swap [Member]
Credit Derivatives [Line Items]
Derivative contracts, barrels	(6,660)
Short
Credit Derivatives [Line Items]
Derivative contracts, barrels	(7,253)
Short | Future
Credit Derivatives [Line Items]
Derivative contracts, barrels	(253)
Short | Swap [Member]
Credit Derivatives [Line Items]
Derivative contracts, barrels	(7,000)