Income taxes - Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current:
Current federal tax expense (benefit)	$ 0	$ (551)	$ (7)
Current state and local tax expense (benefit)	217	(73)	138
Current foreign tax expense (benefit)	638	987	1,013
Total current expense	855	363	1,144
Deferred:
Deferred federal income tax expense (benefit)	(487)	(10,657)	(9,341)
Deferred state and local income tax expense (benefit)	(1,145)	(1,173)	(1,209)
Deferred foreign income tax expense (benefit)	(4,012)	1,512	(627)
Deferred tax benefit	(5,644)	(10,318)	(11,177)
Total income tax benefit	$ (4,789)	$ (9,955)	$ (10,033)