Shareholders' equity (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Jun. 08, 2012
Shareholders' equity (Textual)
Compensation cost attributable to stock options	$ 12,000	$ 54,000
Options exercised, shares	193,400	302,800
Total cash received by stock option exercised during period	79,667	169,496
Common stock, par value	$ 0.01	$ 0.01
Common stock authorized before amendment			10,000,000
Common stock authorized after amendment	12,000,000	12,000,000
Employees and Consultant [Member]
Shareholders' equity (Textual)
Stock awards granted	121,000	117,000
Compensation cost attributable to stock options	306,000	223,000
Options exercised, shares	193,400	302,800
Total cash received by stock option exercised during period	80,000	169,500
Stock issued during period, Value	$ 80,000	$ 169,500
Stock issued during period, Shares	150,562	174,499