Basis of Presentation - Additional Information - Performance Stock Awards (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	400,000	55,477	522,357	88,307
Vesting period			5 years
Non-Plan Stock Option Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expenses, pre-tax	$ 837,000	$ 767,000	$ 1,800,000	$ 1,500,000
Stock-based compensation expenses, after tax	613,000	537,000	1,400,000	1,100,000
Stock-based compensation expenses, per share	$ 0.07	$ 0.06	$ 0.16	$ 0.12
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares			22,250
Vesting period			4 years
Performance Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expenses, pre-tax	$ 69,000	$ 86,000