Business Segment Information - Major Customers (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenue, Major Customer [Line Items]
Sales	$ 1,338,098	$ 532,798	$ 478,434	$ 381,635	$ 373,838	$ 363,753	$ 364,774	$ 312,848	$ 2,730,965	$ 1,415,213	$ 931,736
Occidental Petroleum Corporation
Revenue, Major Customer [Line Items]
Sales									829,081
% of Revenue									30.40%
Plains Marketing, L.P.
Revenue, Major Customer [Line Items]
Sales									426,339	276,285	239,396
% of Revenue									15.60%	19.50%	25.70%
Enterprise Crude Oil Llc
Revenue, Major Customer [Line Items]
Sales									394,162	319,277
% of Revenue									14.40%	22.60%
Conoco Phillips Company
Revenue, Major Customer [Line Items]
Sales											$ 109,358
% of Revenue											11.70%