Summary of All Stock Option Activity (Detail) - Stock Option - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding at December 31, 2014	1,909,456
Granted, Number of Options	190,810
Exercised, Number of Options	(186,622)
Forfeited, Number of Options	(9,656)
Expired, Number of Options	(83,032)
Options Outstanding at December 31, 2015	1,820,956	1,909,456
Options Exercisable at December 31, 2015	1,398,229
Options Outstanding, Weighted Average Grant Date Fair Value	$ 11.79
Granted, Weighted Average Exercise Price	14.16
Exercised, Weighted Average Exercise Price	10.78
Forfeited, Weighted Average Exercise Price	12.16
Expired, Weighted Average Exercise Price	23.55
Options Outstanding, Weighted Average Grant Date Fair Value	11.61	$ 11.79
Options Exercisable,Weighted Average Exercise Price, at December 31, 2015	$ 11.25
Options Outstanding,Weighted Average Remaining Contractual Life	5 years 2 months 12 days	5 years 6 months
Options Exercisable, Weighted Average Remaining Contractual Life, at December 31, 2015	4 years 3 months 18 days
Options Outstanding, Aggregate Intrinsic Value	$ 2.3	$ 3.3
Options Exercisable, Aggregate Intrinsic Value	$ 2.1