Income Per Common Share Computations (Tables)

6 Months Ended

Jun. 30, 2017

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

	Three Months Ended June 30,					Six Months Ended June 30,
(in millions, except per share data)	2017		2016			2017			2016
Numerator for basic income per common share:
Net income	$	78.3	$	69.8		$	85.6		$	72.6
Net income allocated to participating securities	—		(1.3		)	(0.1		)	(1.3		)
Numerator for basic income per common share	$	78.3	$	68.5		$	85.5		$	71.3
Numerator for diluted income per common share	$	78.3	$	69.8		$	85.6		$	72.6
Denominator for basic and diluted net income per common share:
Basic	16.1		16.5			16.2			16.5
Plus dilutive effect of stock awards	0.2		0.2			0.2			0.2
Plus dilutive effect of participating securities	—		0.3			0.1			0.3
Diluted	16.3		17.0			16.5			17.0
Income per common share:
Basic	$	4.86	$	4.16		$	5.27		$	4.32
Diluted	$	4.81	$	4.11		$	5.18		$	4.27