Note receivable (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Note receivable [Abstract]
Interest rate		4.50%	4.50%
Royalty fee payable to be applied towards note receivable balance as it becomes due		$ 100	$ 100
Balance expected to be collected in next twelve months		100	100
Balance expected to be collected thereafter		1,600	1,600
Issuance of note receivable	$ 600		600	$ 1,000
Interest income		18	49
Allowance for loan losses		0	0
Unamortized deferred loan fees and unearned discounts		$ 0	$ 0