Long-Term Incentive Plan (Vested Unit Awards) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Payment Arrangement [Abstract]
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Total Unit Award Accrual Number (in shares)	436,629	317,037	266,028
Fair Value of Unit Awards on Vesting Date (in millions)	$ 31.0	$ 22.1	$ 19.9
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested	$ 27.5	$ 18.1	$ 18.9

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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Period Type:	duration