Earnings Per Common Share (Additional Information) (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Decrease in income attributable to common shareholders	$ 0.2	$ 0.5	$ 0.6	$ 1.2
Option to purchase common stock shares not included in the computation of diluted EPS (in shares)	0.9	0.5	0.9	0.5