Partners’ Equity, Income Allocations and Cash Distributions Cash Distributions (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Capital Unit [Line Items]
Distribution of Available Cash to Unitholders of Record, Period	45 days
Partners' Capital, Distribution Amount Per Share	$ 0.885
General Partner Distributions	$ 1,981,000	$ 1,724,000	$ 1,356,000
General partner incentive distribution	15,519,000	11,181,000	6,737,000
General Partners' Cumulative Cash Distributions	17,500,000	12,905,000	8,093,000
Limited Partners' Capital Account, Distribution Amount	81,508,000	73,223,000	59,725,000
Partners' Capital Account, Regular Quarterly Distributions	99,008,000	86,128,000	67,818,000
Distribution Made to Member or Limited Partner, Distributions Paid, Per Unit	$ 3.48	$ 3.32	$ 3.16
Excess Acquisition Costs, Not Recognized due to Common Control	$ 295,000,000
Minimum Quarterly Distribution [Member]
Capital Unit [Line Items]
Partners Capital, Distribution Amount per Share, Minimum	$ 0.500
First Target Distribution [Member]
Capital Unit [Line Items]
Partners Capital, Distribution Amount per Share, Maximum	$ 0.550
Second Target Distribution [Member]
Capital Unit [Line Items]
Partners Capital, Distribution Amount per Share, Minimum	$ 0.550
Partners Capital, Distribution Amount per Share, Maximum	$ 0.625
Third Target Distribution [Member]
Capital Unit [Line Items]
Partners Capital, Distribution Amount per Share, Minimum	$ 0.625
Partners Capital, Distribution Amount per Share, Maximum	$ 0.750
Thereafter [Member]
Capital Unit [Line Items]
Partners Capital, Distribution Amount per Share, Minimum	$ 0.750
Unitholders [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	98.00%
Unitholders [Member] | Minimum Quarterly Distribution [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	98.00%
Unitholders [Member] | First Target Distribution [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	98.00%
Unitholders [Member] | Second Target Distribution [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	85.00%
Unitholders [Member] | Third Target Distribution [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	75.00%
Unitholders [Member] | Thereafter [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	50.00%
General Partner [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	2.00%
General Partner [Member] | Minimum Quarterly Distribution [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	2.00%
General Partner [Member] | First Target Distribution [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	2.00%
General Partner [Member] | Second Target Distribution [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	15.00%
General Partner [Member] | Third Target Distribution [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	25.00%
General Partner [Member] | Thereafter [Member]
Capital Unit [Line Items]
Marginal Percentage Interest in Distributions	50.00%