Long Term Incentive Plans - Additional Information (Detail) (USD $)	1 Months Ended			12 Months Ended						1 Months Ended
	Dec. 07, 2012	Apr. 26, 2012	May 01, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Incentive Plans	Dec. 31, 2011 Incentive Plans	Dec. 31, 2010 Incentive Plans	Feb. 13, 1997 Stock Options	Apr. 28, 2011 Stock Options Long Term Incentive Plan 2011	Apr. 24, 2002 Stock Options Long Term Incentive Plan 2002	Feb. 13, 1997 Stock Options Maximum	Apr. 28, 2011 Stock Options Maximum Long Term Incentive Plan 2011	Apr. 24, 2002 Stock Options Maximum Long Term Incentive Plan 2002	Dec. 31, 2012 Non Performance Based	Dec. 31, 2012 Performance Based
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options authorized for grant										1,000,000	500,000	500,000
Stock options granted, term										10 years	10 years	10 years
Stock options available for grant per individual employee													400,000	200,000	200,000
Available shares for future issuance				560,000
Options exercised total intrinsic value				$ 250,000	$ 133,000	$ 58,000
Proceeds from exercise of stock options				17,000	167,000	101,000
Excess tax benefit from share-based payment arrangements				259,000	146,000	124,000
Restricted stock vesting period minimum																3 years	1 year
Restricted stock granted annual increments beginning first anniversary of the date of grant				20.00%
Restricted stock granted	57,250	1,000	2,000	60,250	67,600	52,100
Restricted stock weighted average grant date fair value	$ 23.53			$ 23.53	$ 28.43	$ 27.09
Total unrecognized compensation costs				2,700,000
Recognition of compensation cost weighted average period				3 years 9 months 18 days
Total fair value of shares vested				2,300,000
Compensation expense-stock compensation plans				1,222,000	906,000	825,000	1,200,000	906,000	825,000
Total income tax benefit under share-base compensation				$ 297,000	$ 238,000	$ 316,000