Partners' Equity, Cash Distributions (Details) (USD $)	1 Months Ended	3 Months Ended							12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Partners' Capital, Distribution Amount Per Share		$ 0							$ 0
General Partners Capital, Distribution Amount per share		2.00%							2.00%
Distribution of Available Cash to Unitholders, Period									45 days
Partners Capital, Distribution Amount per share Minimum									$ 500
Partner Distributions
General partner interest									2,566,000	1,981,000	1,724,000
General partner incentive distribution									20,986,000	15,519,000	11,181,000
Total general partner distribution									23,552,000	17,500,000	12,905,000
Limited partner distribution									102,222,000	81,508,000	73,223,000
Total regular quarterly cash distribution									125,774,000	99,008,000	86,128,000
Cash distribution per unit applicable to limited partners	$ 0	$ 0.470	$ 0.462	$ 0.455	$ 0.448	$ 0	$ 0	$ 0	$ 1.835	$ 1.740	$ 1.660
Excess Acquisition Costs, Not Recognized due to Common Control		305,600,000							305,600,000
Minimum Quarterly Distribution Percentage [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Partners Capital Distribution percentage		98.00%							98.00%
General Partners Capital, Distribution Amount per share		200.00%							200.00%
First Target Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Partners Capital Distribution percentage		98.00%							98.00%
General Partners Capital, Distribution Amount per share		2.00%							2.00%
Partners Capital, Distribution Amount per share Maximum									550
Second Distribution Target [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Partners Capital Distribution percentage		85.00%							85.00%
General Partners Capital, Distribution Amount per share		15.00%							15.00%
Partners Capital, Distribution Amount per share Minimum									550
Partners Capital, Distribution Amount per share Maximum									625
Third Target Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Partners Capital Distribution percentage		75.00%							75.00%
General Partners Capital, Distribution Amount per share		25.00%							25.00%
Partners Capital, Distribution Amount per share Minimum									625
Partners Capital, Distribution Amount per share Maximum									750
Thereafter Target Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Partners Capital Distribution percentage		50.00%							50.00%
General Partners Capital, Distribution Amount per share		50.00%							50.00%
Partners Capital, Distribution Amount per share Minimum									$ 750