Summary of Stock Option Activity (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Shares
Options outstanding, beginning of year	585,300
Granted
Exercised	(229,600)
Cancelled
Options outstanding, end of year	355,700	[1]
Weighted Average Exercise Price
Options outstanding, beginning of year	$ 14.62
Granted
Exercised	$ 14.85
Cancelled
Options outstanding, end of year	$ 14.47	[1]
Weighted average remaining life
Options outstanding, end of year	2 years 1 month 6 days	[1]
Total Intrinsic value
Options outstanding, end of year	$ 16.7	[1]

[1] All options outstanding are exercisable