Fair Value Measurement (Fair Measurement on a Recurring Nonrecurring Basis) (Details) (Fair Value, Inputs, Level 2 [Member], Commodity Swap [Member], Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Fair Value, Inputs, Level 2 [Member] | Commodity Swap [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Fair value of derivatives	$ 2,727	[1]	$ 1,924	[1]

[1] Unrealized gains or losses on commodity derivatives qualifying for hedge accounting are recorded in AOCI at each measurement date. The fair value of derivative contracts included in assets or liabilities for risk management activities represents the amount at which the instruments could be exchanged in a current arms-length transaction adjusted for credit risk of the Partnership and/or the counterparty as required under FASB ASC 820.