Stock incentive plan - Options outstanding under company's stock incentive plan (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Options
Options outstanding, beginning of period	734	734
Granted	0	0
Forfeited	0	0
Exercised	0	0
Options outstanding, end of period	734	734
Options exercisable, end of period	734	734
Weighted Average Exercise Price
Options outstanding, beginning of period	$ 25.63	$ 25.63
Granted	0	0
Forfeited	0	0
Exercised	0	0
Options outstanding, end of period	25.63	25.63
Fair Value Per Share
Options outstanding, beginning of period	9.76	9.76
Granted	0	0
Forfeited	0	0
Exercised	0	0
Options outstanding, end of period	$ 9.76	$ 9.76
Intrinsic Value Options outstanding	$ 0	$ 0