Represents the number of years used in the calculation of total return to shareholders.

No definition available.

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- Definition

Represents the high end of range of payout depending on achievement of the goals.

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Represents the low end of range of payout depending on achievement of the goals.

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- Definition

Represents the number of shares that could be issued upon vesting of share-based payment awards and achievement of performance goals.

+ References

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- Definition

Represents the number of authorized but unissued shares that could be issued under the equity-based compensation plan.

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No definition available.

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Share-based Compensation Arrangement by Share-based Payment Award, Award Performance Period

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- Definition

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 718
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-Paragraph 2
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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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- Definition

Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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- Definition

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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

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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- Definition

Number of additional shares authorized for issuance under share-based payment arrangement.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Share-based compensation - Narrative (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended
	Jun. 26, 2019	Mar. 01, 2014	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based compensation
Income tax benefit from compensation expense			$ 0.3	$ 0.2	$ 1.2	$ 0.9
Restricted stock units
Share-based compensation
Fair value of vested stock					3.2	2.7
Income tax benefit from compensation expense					0.5	$ 0.4
Unrecognized share based compensation			5.4		$ 5.4
Weighted average period for recognition of unrecognized compensation cost (in years)					2 years 8 months 12 days
Long-term Incentive Plan
Share-based compensation
Payment award, low end of range					0.00%
Payment award, high end of range					200.00%
Award performance period (in years)					3 years
LTIP linked to TRS
Share-based compensation
Unrecognized share based compensation			1.7		$ 1.7
Weighted average period for recognition of unrecognized compensation cost (in years)					1 year 3 months 18 days
Measurement period for total return to shareholders (in years)					3 years
LTIP awards linked to other performance conditions
Share-based compensation
Unrecognized share based compensation			$ 6.1		$ 6.1
Weighted average period for recognition of unrecognized compensation cost (in years)					1 year 2 months 12 days
Equity and Incentive Plan
Share-based compensation
Number of additional shares authorized (in shares)		1,500,000
Shares available for future issuance (in shares)			3,200,000		3,200,000
Number of share issuable upon vesting and achievement of performance goals (in shares)			800,000		800,000
Nonemployee Director Stock Plan
Share-based compensation
Number of additional shares authorized (in shares)	300,000
Shares available for future grant (in shares)			311,027		311,027