Share-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Compensation expense in stock compensation plans	$ 637,887.0	$ 497,614.0	$ 1.3	$ 1.0
Income tax benefit of stock compensation plans	223,260	174,165	462,126	363,484
Unrecognized compensation expense related to nonvested share-based compensation granted under the plan	3,300,000		$ 3,300,000
Weighted average period of unrecognized compensation expense			1 year 3 months 18 days
Cash from option exercises	12,200,000	1,200,000	$ 13,500,000	1,400,000
Tax benefit for tax deductions from option exercises	$ 348,485	$ 52,159	$ 419,735	$ 63,674