Income taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Current:
Federal	$ (428)	$ (124)
State and local	80	31
Current Income Tax Expense (Benefit), Total	(348)	(93)
Deferred
Federal	80	366
State and local	83	383
Deferred Income Tax Expense (Benefit), Total	163	749
(Benefit) expense for income taxes	$ (185)	$ 656