Pensions and other postretirement benefit plans - Multi-Employer Pension Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans
Contributions	$ 1,815	$ 1,789	$ 2,024
CWA/ITU Negotiated Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Contributions	276	369	393
GCIU—Employer Retirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Contributions	42	63	89
The Newspaper Guild International Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Contributions	15	12	92
IAM National Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Contributions	177	188	173
Teamsters Pension Trust Fund of Philadelphia and Vicinity
Defined Benefit Plans and Other Postretirement Benefit Plans
Contributions	1,249	1,098	1,218
Central Pension Fund of the International Union of Operating Engineers and Participating Employers
Defined Benefit Plans and Other Postretirement Benefit Plans
Contributions	$ 56	$ 59	$ 59