Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares
Shares
Options outstanding, beginning of year | shares	301,000
Granted | shares	0
Exercised | shares	(183,700)
Cancelled | shares	(1,700)
Options outstanding, end of year | shares	115,600	[1]
Weighted Average Exercise Price
Options outstanding, beginning of year | $ / shares	$ 9.50
Granted | $ / shares	0
Exercised | $ / shares	9.72
Cancelled | $ / shares	9.00
Options outstanding, end of year | $ / shares	$ 9.16	[1]
Weighted average remaining life
Options outstanding, end of year	8 months 12 days	[1]
Total Intrinsic value
Options outstanding, end of year | $	$ 4.5	[1]

[1] All options outstanding are exercisable