Share-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Compensation expense in stock compensation plans	$ 602,380	$ 807,252	$ 1,200,000	$ 1,600,000
Income tax benefit of stock compensation plans	210,833	282,538	420,068	565,441
Unrecognized compensation expense related to nonvested share-based compensation granted under the plan	2,500,000		$ 2,500,000
Weighted average period of unrecognized compensation expense			1 year 8 months 12 days
Cash from option exercises	652,027	3,400,000	$ 2,200,000	4,100,000
Tax benefit for tax deductions related to option exercises	$ 70,822	$ 243,600	$ 178,356	$ 278,196