Earnings Per Share, Calculation of EPS (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Numerator:
Net income	$ 25.4		$ 29.2		$ 77.5		$ 76.7
Denominator — Weighted-average common shares outstanding (in thousands):
Basic	18,548	[1]	19,154	[1]	18,915	[1]	19,104	[1]
Add: dilutive effect of non-vested common shares, restricted stock units and performance shares	165		134		167		136
Add: dilutive effect of warrants	345		0		185		0
Diluted	19,058		19,288		19,267		19,240
Earnings per common share, Basic:
Net income per share	$ 1.37	[1]	$ 1.52	[1]	$ 4.09	[1]	$ 4.01	[1]
Earnings per common share, Diluted:
Net income per share	$ 1.34		$ 1.51		$ 4.02		$ 3.98

[1] The basic weighted-average number of common shares outstanding during the period excludes non-vested common shares, restricted stock units and performance shares. The diluted weighted-average number of common shares outstanding during the period is calculated using the treasury method.