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Equity and Distributions - Summary of Quarterly Cash Distribution Rates (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified |
3 Months Ended | |||||||||||
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Dec. 31, 2014
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Sep. 30, 2014
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Jun. 30, 2014
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Mar. 31, 2014
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Dec. 31, 2013
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Sep. 30, 2013
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Jun. 30, 2013
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Mar. 31, 2013
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Dec. 31, 2012
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Sep. 30, 2012
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Jun. 30, 2012
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Mar. 31, 2012
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| Equity [Abstract] | ||||||||||||
| Distribution made to member or limited partner, date of declaration | Jan. 26, 2015 | Oct. 23, 2014 | Jul. 24, 2014 | Apr. 24, 2014 | Jan. 27, 2014 | Oct. 22, 2013 | Jul. 18, 2013 | Apr. 18, 2013 | Jan. 15, 2013 | Oct. 19, 2012 | Jul. 19, 2012 | Apr. 19, 2012 |
| Distribution made to member or limited partner, date of record | Feb. 05, 2015 | Nov. 05, 2014 | Aug. 05, 2014 | May 06, 2014 | Feb. 06, 2014 | Nov. 01, 2013 | Aug. 01, 2013 | May 01, 2013 | Feb. 01, 2013 | Nov. 01, 2012 | Aug. 01, 2012 | May 01, 2012 |
| Distribution made to member or limited partner, date of distribution | Feb. 12, 2015 | Nov. 12, 2014 | Aug. 12, 2014 | May 13, 2014 | Feb. 13, 2014 | Nov. 12, 2013 | Aug. 12, 2013 | May 13, 2013 | Feb. 13, 2013 | Nov. 12, 2012 | Aug. 13, 2012 | May 14, 2012 |
| Distribution per unit | $ 0.5500 | $ 0.5500 | $ 0.5500 | $ 0.5500 | $ 0.5500 | $ 0.5500 | $ 0.5125 | $ 0.5125 | $ 0.5075 | $ 0.4950 | $ 0.4800 | $ 0.4800 |
| Aggregate Distribution | $ 46.3 | $ 47.8 | $ 39.5 | $ 33.8 | $ 33.8 | $ 33.8 | $ 22.9 | $ 22.6 | $ 17.4 | $ 11.1 | $ 10.7 | $ 10.7 |
| Distribution Received by Affiliates | $ 3.1 | $ 3.1 | $ 3.0 | $ 3.0 | $ 3.0 | $ 6.9 | $ 6.4 | $ 6.4 | $ 6.3 | $ 6.2 | $ 6.0 | $ 6.0 |