Agreement of Limited Partnership (Details) $ / shares in Units, $ in Millions | Feb. 06, 2017$ / shares | Dec. 31, 2016USD ($)$ / shares | Sep. 30, 2016USD ($)$ / shares | Jun. 30, 2016USD ($)$ / shares | Mar. 31, 2016USD ($)$ / shares | Dec. 31, 2015USD ($)$ / shares | Sep. 30, 2015USD ($)$ / shares | Jun. 30, 2015USD ($)$ / shares | Mar. 31, 2015USD ($)$ / shares | Dec. 31, 2016USD ($)$ / Unit | Dec. 31, 2015USD ($) | Dec. 31, 2014USD ($) |
Agreement of limited partnership | | | | | | | | | | | | |
Payments of distributions to affiliates | $ | | | | | | | | | | $ (257.5) | $ (294.8) | $ (304.1) |
Available cash received from operating partnership (as a percent) | | | | | | | | | | 99.00% | | |
Total distributions declared | $ | | $ 49 | $ 78.8 | $ 39.5 | $ 90.2 | $ 87.5 | $ 70.8 | $ 60.4 | $ 76.1 | | | |
Number of average trading days' closing prices used to determine the purchase price of outstanding units of non-affiliates | | | | | | | | | | 20 days | | |
Number of days before the purchase announcement is made, as a basis for determining the purchase price of outstanding units of non-affiliates | | | | | | | | | | 5 days | | |
Minimum Quarterly Distributions | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Target Limit | | | | | | | | | | 0.605 | | |
Target Increment | | | | | | | | | | 0.605 | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 100.00% | | |
First Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Target Limit | | | | | | | | | | 0.715 | | |
Target Increment | | | | | | | | | | 0.110 | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 100.00% | | |
Second Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Target Limit | | | | | | | | | | 0.825 | | |
Target Increment | | | | | | | | | | 0.110 | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 100.00% | | |
Third Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Target Limit | | | | | | | | | | 1.045 | | |
Target Increment | | | | | | | | | | 0.220 | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 100.00% | | |
Final Target and Beyond | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Target Increment | | | | | | | | | | 0 | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 100.00% | | |
Final Target and Beyond | Minimum | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Target Limit | | | | | | | | | | 1.045 | | |
Common and Class B Common Units | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Cash distribution made, excluding when cumulative distribution is specified, (as a percent) | | | | | | | | | | 99.975% | | |
Common Units | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Declared partnership distributions | $ | | $ 32.7 | $ 47.7 | $ 28 | $ 53.3 | $ 52 | $ 43.6 | $ 38.5 | $ 46.3 | | | |
Cash distribution declared per common limited partnership unit (in dollars per unit) | $ / shares | | $ 1.77 | $ 2.58 | $ 1.51 | $ 2.88 | $ 2.81 | $ 2.36 | $ 2.08 | $ 2.50 | | | |
Common Units | Minimum Quarterly Distributions | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 98.99% | | |
Common Units | First Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 98.99% | | |
Common Units | Second Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 85.859% | | |
Common Units | Third Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 75.758% | | |
Common Units | Final Target and Beyond | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 50.505% | | |
Class B Common Units | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Declared partnership distributions | $ | | $ 0.5 | $ 0.7 | $ 0.4 | $ 0.9 | $ 0.9 | $ 0.7 | $ 0.6 | $ 0.7 | | | |
Cash distribution declared per common limited partnership unit (in dollars per unit) | $ / shares | | $ 2.60 | $ 4.17 | $ 2.09 | $ 4.78 | $ 4.64 | $ 3.74 | $ 3.20 | $ 4.03 | | | |
Class B Common Units | Minimum Quarterly Distributions | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 0.985% | | |
Class B Common Units | First Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 0.985% | | |
Class B Common Units | Second Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 0.985% | | |
Class B Common Units | Third Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 0.985% | | |
Class B Common Units | Final Target and Beyond | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 0.985% | | |
Subsequent Event | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Cash distribution declared per common limited partnership unit (in dollars per unit) | $ / shares | $ 1.22 | | | | | | | | | | | |
General Partner's Interests | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Available cash distributed from operating partnership to General Partner (as a percent) | | | | | | | | | | 1.00% | | |
Cash distribution made, excluding when cumulative distribution is specified, (as a percent) | | | | | | | | | | 0.025% | | |
Partnership equity interest (as a percent) | | 1.00% | | | | | | | | 1.00% | | |
Declared partnership distributions | $ | | $ 15.8 | $ 30.4 | $ 11.1 | $ 36 | $ 34.6 | $ 26.5 | $ 21.3 | $ 29.1 | | | |
Percentage of outstanding units owned by the General Partner and its affiliates | | 75.10% | | | | | | | | 75.10% | | |
Period within which highest price is paid for any unit preceding the date the purchase is announced used to determine the purchase price of outstanding units of non-affiliates | | | | | | | | | | 90 days | | |
General Partner's Interests | Minimum | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Percentage of ownership of non-affiliates of the General Partner allowing majority owner to acquire outstanding units held by non-affiliated persons | | | | | | | | | | 25.00% | | |
Notice period for making decision to purchase the outstanding units | | | | | | | | | | 30 days | | |
General Partner's Interests | Maximum | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Notice period for making decision to purchase the outstanding units | | | | | | | | | | 60 days | | |
General Partner's Interests | Minimum Quarterly Distributions | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 0.025% | | |
General Partner's Interests | First Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 0.025% | | |
General Partner's Interests | Second Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 13.156% | | |
General Partner's Interests | Third Target | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 23.257% | | |
General Partner's Interests | Final Target and Beyond | | | | | | | | | | | | |
Agreement of limited partnership | | | | | | | | | | | | |
Income and distribution allocation (as a percent) | | | | | | | | | | 48.51% | | |