Stock options and awards (Details) - Employee Stock Option [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of outstanding options, exercisable options, exercise price, expiration date, weighted average remaining life under company stock option plans [Abstract]
Shares Underlying Options Outstanding	50,000	60,000	100,000
Shares Underlying Exercisable Options	50,000	60,000
Exercise Price	$ 1.24	$ 1.15
Weighted Average Remaining Life	7 months 6 days	1 year 6 months
1/11/09 [Member]
Summary of outstanding options, exercisable options, exercise price, expiration date, weighted average remaining life under company stock option plans [Abstract]
Date Granted	Jan. 11, 2009	Jan. 11, 2009
Shares Underlying Options Outstanding	30,000	40,000
Shares Underlying Exercisable Options	30,000	40,000
Exercise Price	$ 0.69	$ 0.69
Expiration Date	Jan. 10, 2019	Jan. 10, 2019
Weighted Average Remaining Life	0 years	1 year
4/26/10 [Member]
Summary of outstanding options, exercisable options, exercise price, expiration date, weighted average remaining life under company stock option plans [Abstract]
Date Granted	Apr. 26, 2010	Apr. 26, 2010
Shares Underlying Options Outstanding	20,000	20,000
Shares Underlying Exercisable Options	20,000	20,000
Exercise Price	$ 2.07	$ 2.07
Expiration Date	Apr. 25, 2020	Apr. 25, 2020
Weighted Average Remaining Life	1 year 3 months 19 days	2 years 4 months 24 days