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, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Numerator:
Net income	$ 29.2		$ 4.1		$ 76.7		$ 19.0	[1]
Denominator - Weighted-average common shares outstanding (in thousands):
Basic	19,154	[2]	18,999	[2]	19,104	[2]	18,971	[2]
Diluted	19,288	[2]	19,197	[2]	19,240	[2]	19,171	[2]
Earnings per common share, Basic:
Net income per share	$ 1.52		$ 0.21		$ 4.01		$ 1.00
Earnings per common share, Diluted:
Net income per share	$ 1.51		$ 0.21		$ 3.98		$ 0.99	[3]

[1] Total comprehensive income and components of other comprehensive income (loss) were previously included in the Statement of Stockholders' Equity for interim reporting periods prior to 2012. The Company adopted ASU No. 2011-05, Comprehensive Income (Topic 220): Presentation of Comprehensive Income, beginning with the annual period ended December 31, 2011 and presented the Statement of Comprehensive Income as its own separate statement. As such, the "Previously Reported" column reflects the changes in the presentation.

[2] 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.

[3] Beginning 2012, the Company presented diluted earnings per share under the treasury method because it became more dilutive than the diluted earnings per share under the two-class method. As such, restated diluted earnings per share for the quarter and nine months ended September 30, 2011 were calculated based on the treasury method to conform to current period presentation. Previously reported diluted earnings per share for the quarter and nine months ended September 30, 2011 are based on the two-class method. The "Adjustment" column reflects the difference between restated diluted earnings per share using the two-class method and the previously reported diluted earnings per share.