Employees, Retirement and Incentive Plans Restricted Units (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Share-based Compensation Arrangements
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 200,000
Restricted and Phantom Units
Share-based Compensation Arrangements
Nonvested restricted units outstanding	130,981		145,205
Vesting and transfer of common units to recipients	5,646	0
Vested in Period	$ 29.94
Weighted average grant date fair value	$ 26.11		$ 26.22
Forfeitures	8,578
Weighted Average Grant Date Fair Value - Forfeitures	$ 25.47
Total unrecognized compensation related to nonvested units	$ 0.9
Weighted average remaining contractual term (years)	1 year 1 month 6 days
Performance Shares
Share-based Compensation Arrangements
Nonvested restricted units outstanding	41,811		53,445
Vesting and transfer of common units to recipients	11,634
Total unrecognized compensation related to nonvested units	$ 0.4
Weighted average remaining contractual term (years)	1 year 3 months 18 days

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Number of shares under non-option equity instrument agreements that were cancelled as a result of occurrence of a terminating event.

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