Activity of Exercisable Common Stock Options (Detail) - Stock Options - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Number of Shares
Exercisable common stock options, beginning balance	986,300	543,867	181,327
Common stock options exercised	(242,050)	(150,000)	(20,668)
Common stock options vested	31,400	592,433	383,208
Exercisable common stock options, ending balance	775,650	986,300	543,867
Weighted Average Exercise Price Per Share
Exercisable common stock options, beginning balance	$ 6.08	$ 5.76	$ 5.21
Common stock options exercised	5.16	5.72	3.00
Common stock options vested	3.84	6.29	5.47
Exercisable common stock options, ending balance	$ 6.28	$ 6.08	$ 5.76