Related-Party Transactions Related-Party Transactions, Summary of Affiliate Transactions (Details) - USD ($) $ / shares in Units, $ in Millions |
3 Months Ended | 12 Months Ended | ||||||
|---|---|---|---|---|---|---|---|---|
May 15, 2017 |
Apr. 19, 2017 |
Mar. 31, 2017 |
Mar. 31, 2016 |
Dec. 31, 2016 |
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| Distribution Made to Limited Partner, Cash Paid | $ 77.0 | |||||||
| Distribution Made to Limited Partner, Distributions Declared, Per Unit | $ 0.94 | [1] | $ 0.91 | |||||
| Distribution Made to Limited Partner, Distribution Date | Feb. 14, 2017 | |||||||
| Distribution Made to Limited Partner, Cash Distributions Paid | $ 94.0 | $ 73.0 | ||||||
| Subsequent Event | ||||||||
| Distribution Made to Limited Partner, Declaration Date | Apr. 19, 2017 | |||||||
| Distribution Made to Limited Partner, Distribution Date | [1] | May 15, 2017 | ||||||
| Distribution Made to Limited Partner, Cash Distributions Paid | $ 71.0 | |||||||
| Rockies Natural Gas Business Acquisition [Member] | ||||||||
| managing member or general partner, subsequent distribution amount forfeited | $ 12.5 | |||||||
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