Activity of Exercisable Common Stock Options (Detail) - Stock Options - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of Shares
Exercisable common stock options, beginning balance	775,650	986,300	543,867
Common stock options exercised	(27,500)	(242,050)	(150,000)
Common stock options vested		31,400	592,433
Exercisable common stock options, ending balance	748,150	775,650	986,300
Weighted Average Exercise Price Per Share
Exercisable common stock options, beginning balance	$ 6.28	$ 6.08	$ 5.76
Common stock options exercised	4.76	5.16	5.72
Common stock options vested		3.84	6.29
Exercisable common stock options, ending balance	$ 6.33	$ 6.28	$ 6.08