Stockholders' equity and earnings per share (Details) (Stock Options, USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Stock Options
Number of options:
Number of options outstanding, beginning	87,500	87,500
Number of options granted
Number of options cancelled
Number of options exercised
Number of options forfeited
Number of options expired
Number of options outstanding, ending	87,500	87,500
Number of options exercisable	87,500	87,500
Weighted Average Exercise Price of options outstanding, beginning	$ 4.80	$ 4.80
Weighted Average Exercise Price of options granted
Weighted Average Exercise Price of options cancelled
Weighted Average Exercise Price of options exercised
Weighted Average Exercise Price of options forfeited
Weighted Average Exercise Price of options expired
Weighted Average Exercise Price of options outstanding, ending	$ 4.80	$ 4.80
Weighted Average Exercise Price of options exercisable	$ 4.80	$ 4.80
Weighted Average Remaining Contractual Term:
Weighted Average Remaining Contractual Term of Options outstanding, beginning		5 years 0 months 29 days
Weighted Average Remaining Contractual Term of options outstanding, ending	3 years 9 months 29 days	4 years 0 months 29 days