Summary of Significant Accounting Policies - Derivative Instruments (Details) - Cash Flow Hedging - Interest Rate Swap $ in Millions	9 Months Ended
Sep. 30, 2017 USD ($)	Sep. 30, 2018 instruments
Derivative [Line Items]
Outstanding interest rate swap contracts designated as cash flow hedges \| instruments		5
Derivative, net hedge ineffectiveness gain (loss) \| $	$ 0.2

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of gain (loss) from the ineffectiveness of the hedge.

+ References

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The number of derivative instruments of a particular group held by the entity.

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