Stock-Based Compensation - Option Activity under the Company's Stock Option Plans (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Balance at beginning of period	102,216
Granted	0
Exercised	(34,728)
Expired	0
Forfeited	0
Balance at end of period	67,488	102,216
Options exercisable at year-end	67,488
Weighted Average Exercise Price
Balance beginning of period	$ 8.49
Granted	0.00
Exercised	8.84
Expired	0.00
Forfeited	0.00
Balance end of period	8.28	$ 8.49
Options exercisable at year-end	$ 8.28
Outstanding, Weighted average remaining contractual term (in years), Ending balance	2 years 10 months 10 days	4 years 3 months 7 days
Options exercisable, Weighted average remaining contractual term (in years), Ending balance	2 years 10 months 10 days
Outstanding, Aggregate intrinsic value	$ 440,483	$ 1,101,806
Options exercisable at year end, Aggregate intrinsic value	$ 440,483