Stock-based compensation arrangements (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Stock-based compensation expense	$ 191,828	$ 227,091
Stock option grants beginning of period [Member]
Stock-based compensation expense	182,064	139,272
Stock option grants [Member]
Stock-based compensation expense	6,188	79,897
Employee Stock Purchase Plan [Member]
Stock-based compensation expense	1,332	5,647
Director Agreements [Member]
Stock-based compensation expense	$ 2,244	$ 2,275