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Basis of Presentation and Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basis of Presentation and Summary of Significant Accounting Policies
Ownership interest held by public unitholders in the reporting entity (as a percent)	69.00%
Concentration of credit risk
Minimum period after receivable balances are past due that significant accounts are reviewed individually for collectibility	90 days
Bad debt expense	$ 494	$ 83	$ 1,292

Amount of the current period expense charged against operations, the offset which is generally to the allowance for doubtful accounts for the purpose of reducing receivables, including notes receivable, to an amount that approximates their net realizable value (the amount expected to be collected).

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