Commitments and Contingencies - Purchase and sales commitments (Details) bbl in Thousands, $ in Thousands	Mar. 31, 2016 USD ($) bbl
Fixed Price Sales [Member]
Summary Of Purchase And Sale Commitments
Sale commitments, Volume (barrels) | bbl	3,613
Sale commitments, Value | $	$ 128,923
Floating Price Sales [Member]
Summary Of Purchase And Sale Commitments
Sale commitments, Volume (barrels) | bbl	19,915
Sale commitments, Value | $	$ 678,336
Fixed Price Purchases [Member]
Summary Of Purchase And Sale Commitments
Purchase commitments, Volume (barrels) | bbl	2,459
Purchase commitments, Value | $	$ 86,203
Floating Price Purchases [Member]
Summary Of Purchase And Sale Commitments
Purchase commitments, Volume (barrels) | bbl	15,214
Purchase commitments, Value | $	$ 579,964