Earnings Per Share, Calculation of EPS (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Numerator:
Net income	$ 18.6		$ 21.0		$ 52.1		$ 47.5
Denominator — Weighted-average common shares outstanding (in thousands):
Basic	18,742	[1]	19,137	[1]	19,027	[1]	19,087	[1]
Add: dilutive effect of restricted stock, restricted stock units and performance shares	112		63		135		83
Add: dilutive effect of warrants	91		0		94		0
Diluted	18,945	[1]	19,200	[1]	19,256	[1]	19,170	[1]
Earnings per common share, Basic:
Net income per share	$ 0.99		$ 1.10		$ 2.73		$ 2.49
Earnings per common share, Diluted:
Net income per share	$ 0.98		$ 1.09		$ 2.70		$ 2.48

[1] The basic weighted-average number of common shares outstanding during the period excludes unvested share-based payment awards. The diluted weighted-average number of common shares outstanding during the period is calculated using the treasury method.