Stock Based Compensation - Summary of Stock Options Outstanding (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, Number of options	102,000
Option outstanding, Average life	5 years 8 months 12 days
Options outstanding, Weighted average exercise price	$ 28.89
Options exercisable, Number of options	102,000
Options exercisable, Weighted average exercise price	$ 28.89
Range One [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise prices, Higher Range	$ 12.63
Options outstanding, Number of options	6,000
Option outstanding, Average life	9 months 18 days
Options outstanding, Weighted average exercise price	$ 12.63
Options exercisable, Number of options	6,000
Options exercisable, Weighted average exercise price	$ 12.63
Range Two [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise prices, Lower Range	$ 20.16
Exercise prices, Higher Range	$ 22.95
Options outstanding, Number of options	32,000
Option outstanding, Average life	5 years 9 months 18 days
Options outstanding, Weighted average exercise price	$ 21.59
Options exercisable, Number of options	32,000
Options exercisable, Weighted average exercise price	$ 21.59
Range Three [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise prices, Lower Range	$ 25.18
Exercise prices, Higher Range	$ 26.86
Options outstanding, Number of options	22,000
Option outstanding, Average life	6 years 4 months 24 days
Options outstanding, Weighted average exercise price	$ 25.79
Options exercisable, Number of options	22,000
Options exercisable, Weighted average exercise price	$ 25.79
Range Four [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise prices, Lower Range	$ 37.23
Exercise prices, Higher Range	$ 40.46
Options outstanding, Number of options	42,000
Option outstanding, Average life	6 years
Options outstanding, Weighted average exercise price	$ 38.40
Options exercisable, Number of options	42,000
Options exercisable, Weighted average exercise price	$ 38.40