Net Income Per Share (Tables)

3 Months Ended

Mar. 31, 2017

Earnings Per Share [Abstract]

Reconciliation of the Common and Potential Common Shares Outstanding Used in Earnings Per Share Calculation

A reconciliation of the average number of common and potential common shares outstanding used in the calculations of basic and diluted net income per share follows ($ in millions, shares in thousands):

	Three Months Ended
	March 31, 2017			March 31, 2016
Numerator (basic and diluted):
Net income	$	13.7		$	21.1
Less: Dividends paid to participating securities	(0.1		)	(0.1		)
Less: Undistributed earnings available to participating securities	—			—
Undistributed and distributed earnings available to common stockholders	$	13.6		$	21.0
Denominator:
Average number of common shares outstanding	30,364.7			30,294.9
Effect of dilutive stock-based compensation	122.6			127.8
Average number of common and potential common shares outstanding	30,487.3			30,422.7