Stock-based compensation arrangements (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Stock-based compensation expense	$ 29,595	$ 48,357	$ 60,284	$ 96,131
Stock option grants beginning of period [Member]
Stock-based compensation expense	25,243	48,185	51,965	94,796
Stock option grants [Member]
Stock-based compensation expense	3,061	3	6,110	3
Employee Stock Purchase Plan [Member]
Stock-based compensation expense	$ 1,291	$ 169	$ 2,208	$ 1,332