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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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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No definition available.

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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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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.

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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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Stock-Based Compensation - Restricted Stock Award and RSU Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted stock awards
Restricted stock, Shares Subject to Restriction
Outstanding at the beginning of the period (in shares)	24,633
Vested (in shares)	(24,633)
Outstanding at the end of the period (in shares)		24,633
Restricted stock, Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 19.82
Vested (in dollars per share)	$ 19.82
Outstanding at the end of the period (in dollars per share)		$ 19.82
Additional share-based compensation disclosures
Total fair value of shares vested	$ 0.5	$ 1.8	$ 2.3
Restricted stock units
Restricted stock, Shares Subject to Restriction
Outstanding at the beginning of the period (in shares)	806,249
Granted (in shares)	366,526
Vested (in shares)	(268,014)
Forfeited (in shares)	(39,660)
Outstanding at the end of the period (in shares)	865,101	806,249
Restricted stock, Weighted Average Grant Date Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 29.88
Granted (in dollars per share)	41.07
Vested (in dollars per share)	29.47
Forfeited (in dollars per share)	30.12
Outstanding at the end of the period (in dollars per share)	$ 34.73	$ 29.88
Additional share-based compensation disclosures
Total fair value of shares vested	$ 7.9	$ 6.9	$ 2.0
Unrecognized pre-tax stock-based compensation expense	$ 23.0
Weighted average remaining service period	2 years 10 months 24 days
Minimum \| Restricted stock awards
Additional share-based compensation disclosures
Period of service restrictions	1 year
Minimum \| Restricted stock units
Additional share-based compensation disclosures
Period of service restrictions	1 year
Maximum \| Restricted stock awards
Additional share-based compensation disclosures
Period of service restrictions	4 years
Maximum \| Restricted stock units
Additional share-based compensation disclosures
Period of service restrictions	4 years