Net Income (Loss) Per Common Share (Net Income (Loss) Per Common Share On Basic And Diluted Basis) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share [Line Items]
Net income (loss)	$ 13.4	$ (10.8)	$ 57.0	$ (83.3)
Weighted average common shares outstanding - basic	25,227,194	27,237,788	25,694,761	27,374,953
Equity compensation awards	529,689	0	406,973	0
Weighted average common shares outstanding - diluted	25,756,883	27,237,788	26,101,734	27,374,953
Net income (loss) per common share - basic	$ 0.53	$ (0.39)	$ 2.22	$ (3.04)
Net income (loss) per common share - diluted	$ 0.52	$ (0.39)	$ 2.18	$ (3.04)