Nature of operations and summary of significant accounting policies (Stock-based Compensation) (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) tranche installment
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	1 year
Time Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of vesting annual installments | installment	3
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of tranches | tranche	3
Award vesting period (in years)	3 years
Shares based awards expense recognized | $	$ 0