Financing Financing - Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Capital Unit [Line Items]
Number of common units registered for resale under Amended and Restated Registration Rights Agreement (in number of units)	27.9
Maximum amount Partnership must pay for reimbursement of underwriting discounts and commissions (in dollars per unit)	$ 0.914
Registration Payment Arrangement, Accrual Carrying Value	$ 0.0	$ 16.0