Stockholders' equity Class of Rights and Warrants (Details) (USD $)	12 Months Ended				0 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 09, 2010	Feb. 22, 2012 February 22, 2013	Dec. 31, 2013 December 14, 2015	Dec. 31, 2013 January 15, 2016	Jan. 15, 2011 January 15, 2016
Class of Warrant or Right [Line Items]
Number of Warrants Granted (in shares)	0	50,000			50,000
Warrants, Exercise Price Per Share				$ 3.25	$ 3.00	$ 3.25		$ 2.69
Number of Warrants Outstanding (in shares)	507,500	565,500	588,000			500,000	7,500
Warrants Exercised Expire Date					Feb. 22, 2013	Dec. 14, 2015
Payments for Repurchase of Common Stock	$ 0	$ 750,000			$ 7,500