Earnings Per Share, Calculation of EPS (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Numerator:
Net income	$ 27.3	$ 25.4	$ 18.6	$ 33.5	$ 9.1	$ 29.2	$ 21.0	$ 26.5	$ 104.8		$ 85.8		$ 25.1
Denominator - Weighted-average common shares outstanding (in thousands):
Basic									18,827	[1]	19,115	[1]	18,979	[1]
Add: dilutive effect of non-vested common shares, restricted stock units and performance shares									178		163		0
Add: dilutive effect of warrants									241		0		0
Diluted									19,246	[2],[3]	19,278	[2],[3]	18,979	[2],[3]
Earnings per common share, Basic:
Net income per share	$ 1.48	$ 1.37	$ 0.99	$ 1.75	$ 0.48	$ 1.52	$ 1.10	$ 1.39	$ 5.56		$ 4.49		$ 1.32
Earnings per common share, Diluted:
Net income per share	$ 1.44	$ 1.34	$ 0.98	$ 1.73	$ 0.47	$ 1.51	$ 1.09	$ 1.38	$ 5.44	[2],[3]	$ 4.45	[2],[3]	$ 1.32	[2],[3]

[1] The basic weighted-average number of common shares outstanding during the period excludes unvested share-based incentive awards.

[2] The diluted weighted-average number of common shares outstanding and diluted earnings per share for 2013 and 2012 were calculated using the treasury method. The diluted weighted-average number of common shares outstanding and diluted earnings per share for 2011 were calculated using the two-class method (see Note 1).

[3] Diluted weighted-average number of common shares outstanding and diluted earnings per share for 2013 and 2012 are based on the treasury method. Diluted weighted-average number of common shares outstanding and diluted earnings per share for 2011 is based on the two-class method (see Note 1 and Note 13).