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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Numerator:
Net income	$ 15.6	$ 15.9	$ 24.5	$ 15.8	$ 27.3	$ 25.4	$ 18.6	$ 33.5	$ 71.8	$ 104.8		$ 85.8
Denominator - Weighted-average common shares outstanding (in thousands):
Basic									17,818	18,827	[1]	19,115	[1]
Add: dilutive effect of non-vested common shares, restricted stock units and performance shares									179	178		163
Add: dilutive effect of warrants									596	241		0
Diluted									18,593	19,246	[2]	19,278	[2]
Net income per common share:
Basic	$ 0.88	$ 0.90	$ 1.38	$ 0.88	$ 1.48	$ 1.37	$ 0.99	$ 1.75	$ 4.02	$ 5.56		$ 4.49
Earnings per common share, Diluted:
Net income per share	$ 0.85	$ 0.85	$ 1.33	$ 0.85	$ 1.44	$ 1.34	$ 0.98	$ 1.73	$ 3.86	$ 5.44	[2]	$ 4.45	[2]

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

[2] The diluted weighted-average number of common shares outstanding during the periods were calculated using the treasury method.