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

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

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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 number of grants made 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 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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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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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An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

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Number of grantees affected by modification of award under share-based payment arrangement.

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Equity Incentive Program Equity Incentive Program - PSUs (Details) - Performance Shares $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($) $ / shares shares	Jun. 30, 2020 numberOfGrantees	Jun. 30, 2019 numberOfGrantees	Jun. 30, 2018 numberOfGrantees
Share-based Compensation Arrangement by Share-based Payment Award
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount \| $	$ 14.3
Number of Shares [Roll Forward]
Beginning balance \| shares	920,973
Granted \| shares	277,183
Vested (1) \| shares	(329,092)
Forfeited \| shares	(84,493)
Ending balance \| shares	784,571
Weighted Average Grant Date Fair Value
Beginning balance \| $ / shares	$ 16.04
Granted \| $ / shares	28.46
Vested (1) \| $ / shares	13.75
Forfeited \| $ / shares	17.16
Ending balance \| $ / shares	$ 21.27
Share-based Payment Arrangement, Plan Modification, Number of Grantees Affected \| numberOfGrantees		8	8	9
2019
Weighted Average Grant Date Fair Value
Share-based Payment Arrangement, Plan Modification, Incremental Cost \| $	$ 2.4
2018
Weighted Average Grant Date Fair Value
Share-based Payment Arrangement, Plan Modification, Incremental Cost \| $	3.9
2020
Weighted Average Grant Date Fair Value
Share-based Payment Arrangement, Plan Modification, Incremental Cost \| $	$ 4.7