Share-Based Compensation - Stock Options Exercise Data (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Summary of stock option exercise data
Cash received from options exercised		$ 9.9	$ 15.5
Stock Options
Summary of stock option exercise data
Number of options exercised (in shares)	4,857	191,508	287,760
Cash received from options exercised	$ 0.6	$ 9.9	$ 15.5
Total intrinsic value of options exercised	$ 0.1	$ 11.5	$ 17.0

Amount of cash inflow from exercise of option under share-based payment arrangement.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Number of share options (or share units) exercised during the current period.

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