Share-Based Compensation - Option Activity under the Company's Stock Option Plans (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Number of Shares
Outstanding, Number of shares, Beginning balance (in shares)	67,488
Granted, Number of shares (in shares)	0	0
Exercised, Number of shares (in shares)	0
Forfeited, Number of shares (in shares)	0
Expired, Number of shares (in shares)	0
Outstanding, Number of shares, Ending balance (in shares)	67,488		67,488
Options exercisable, Number of shares, Ending balance (in shares)	67,488
Weighted Average Exercise Price
Outstanding, Weighted average exercise price, Beginning balance (in usd per share)	$ 8.28
Granted, Weighted average exercise price (in usd per share)	0.00
Exercised, Weighted average exercise price (in usd per share)	0.00
Forfeited, Weighted average exercise price (in usd per share)	0.00
Expired, Weighted average exercise price (in usd per share)	0.00
Outstanding, Weighted average exercise price, Ending balance (in usd per share)	8.28		$ 8.28
Options exercisable, Weighted average exercise price, Ending balance (in usd per share)	$ 8.28
Weighted Average Remaining Contractual Term (in years)
Outstanding, Average remaining contractual term (in years)	2 years 7 months 10 days		2 years 10 months 10 days
Options exercisable, Average remaining contractual term (in years)	2 years 7 months 10 days
Aggregate Intrinsic Value
Outstanding, Aggregate intrinsic value	$ 448,581		$ 440,483
Options exercisable at year end, Aggregate intrinsic value	$ 448,581