Share-based compensation - 2011 Director Plan (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based compensation
Income tax benefit	$ 0.4	$ 0.7	$ 0.7	$ 0.9
Common stock
Share-based compensation
Shares granted (in shares)	35,632	35,580	36,100	35,580
Fair value	$ 1.3	$ 1.5	$ 1.3	$ 1.5
Income tax benefit	$ 0.3	$ 0.4	$ 0.3	$ 0.4

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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Number of shares issued under share-based payment arrangement.

+ References

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