Stockholders' Equity - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Numerator used in basic and diluted EPS:
Net income	$ 171.7	$ 134.4
Denominator:
Weighted average number of common shares used in basic EPS (in shares)	162,894,306	163,528,343
Effect of dilutive shares:
Potential common shares issuable from stock options and stock awards (in shares)	2,829,814	3,016,602
Weighted average number of common shares and dilutive potential common shares used in diluted EPS (in shares)	165,724,120	166,544,945

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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