Income taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ (124)	$ (507)
State and local	31	(167)
Current Income Tax Expense (Benefit), Total	(93)	(674)
Deferred
Federal	366	(693)
State and local	383	(337)
Deferred Income Tax Expense (Benefit), Total	749	(1,030)
(Benefit) expense for income taxes	$ 656	$ (1,704)