Business Segment Information - Major Customers (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue, Major Customer [Line Items]
Sales	$ 143,642	$ 180,152	$ 229,607	$ 215,308	$ 346,881	$ 394,107	$ 374,714	$ 443,056	$ 768,709	$ 1,558,758	$ 1,983,388
Plains Marketing, L.P.
Revenue, Major Customer [Line Items]
Sales									$ 318,018	$ 597,117	$ 491,258
Percentage of revenue									41.40%	38.30%	24.80%
Shell Trading (US) Company
Revenue, Major Customer [Line Items]
Sales											$ 347,422
Percentage of revenue											17.50%
Targa Pipeline Mid-Continent West OK LLC [Member]
Revenue, Major Customer [Line Items]
Sales									$ 231,649	$ 333,027	$ 211,838
Percentage of revenue									30.10%	21.40%	10.70%