Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Derivatives (Details) $ in Millions	3 Months Ended		9 Months Ended
Derivatives (Details) $ in Millions	Sep. 30, 2019 USD ($)	Jun. 30, 2018 USD ($) instrument	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 GBP (£)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 GBP (£)
Derivative [Line Items]
Notional amount	$ 39.2		$ 39.2
Loss on derivative instruments	1.9		1.9
Loss on foreign currency forward transactions		$ 29.0		$ 29.0
Foreign Currency Forward
Derivative [Line Items]
Notional amount \| £					£ 50,000,000.0		£ 46,000,000.0
Loss on derivative instruments	2.4		4.0
Number of foreign currency forward transactions \| instrument		2
Foreign Currency Forward \| Other Current Liabilities
Derivative [Line Items]
Derivative liability	$ 2.9		$ 2.9			$ 3.8