Financial risk management objectives and policies - Reconciliation of Adjusted EBITDA (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Financial Instruments [Abstract]
Operating profit	$ 19.3	$ 35.8	$ 37.9
Profit on sale of redundant site (Note 5)	(0.4)	(2.1)	0.0
Changes to defined benefit pension plans (Note 5)	0.0	(0.6)	(18.0)
Restructuring and other expense (Note 5)	21.6	2.2	22.4
Loss on disposal of property, plant and equipment	0.1	0.2	0.0
Other share based compensation charges	2.2	1.4	1.3
Depreciation and amortization	19.0	18.4	18.6
Adjusted EBITDA	61.8	55.3	62.2
Bank and other loans	108.8	121.0	131.6
Less: Cash and cash equivalents	(13.3)	(13.6)	(36.9)
Add: Overdrafts	4.2	0.0	0.0
Add: Restricted cash	0.7	0.0	0.0
Net debt	$ 100.4	$ 107.4	$ 94.7
Net debt: Adjusted EBITDA ratio	1.6	1.9	1.5

The amount that has been withdrawn from an account in excess of existing cash balances. This is considered a short-term extension of credit by the bank. [Refer: Cash and cash equivalents]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2017-01-01
-Paragraph 45
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2017-03-01&anchor=para_45&doctype=Standard
-URIDate 2017-03-09