Commitments and Contingencies - Purchase and sales commitments (Details) bbl in Thousands, $ in Thousands	Jun. 30, 2016 USD ($) bbl
Fixed Price Sales [Member]
Summary Of Purchase And Sale Commitments
Sale commitments, Volume (barrels) | bbl	4,563
Sale commitments, Value | $	$ 218,212
Floating Price Sales [Member]
Summary Of Purchase And Sale Commitments
Sale commitments, Volume (barrels) | bbl	17,773
Sale commitments, Value | $	$ 786,992
Fixed Price Purchases [Member]
Summary Of Purchase And Sale Commitments
Purchase commitments, Volume (barrels) | bbl	3,528
Purchase commitments, Value | $	$ 167,030
Floating Price Purchases [Member]
Summary Of Purchase And Sale Commitments
Purchase commitments, Volume (barrels) | bbl	12,701
Purchase commitments, Value | $	$ 601,820