Commitments and contingencies - Non-cancelable operating leases (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Commitments and contingencies
Annual Rent	$ 1,700,000	$ 2,600,000	$ 3,100,000
Baton Rouge Louisiana
Commitments and contingencies
Lease Expiration Date	May 01, 2024
Annual Rent	$ 30,000
Champaign, Illinois
Commitments and contingencies
Lease Expiration Date	Dec. 01, 2024
Annual Rent	$ 609,000
Champaign, Illinois (2nd location)
Commitments and contingencies
Lease Expiration Date	Sep. 01, 2026
Annual Rent	$ 349,000
Charlotte, North Carolina
Commitments and contingencies
Lease Expiration Date	May 01, 2025
Annual Rent	$ 38,000
Escondido,California
Commitments and contingencies
Lease Expiration Date	Jun. 01, 2027
Annual Rent	$ 238,000
Long Beach California
Commitments and contingencies
Lease Expiration Date	Feb. 01, 2024
Annual Rent	$ 28,800
Ontario, California
Commitments and contingencies
Lease Expiration Date	Dec. 01, 2024
Annual Rent	$ 174,000
Riverside, California
Commitments and contingencies
Lease expiration period description	Month to Month
Annual Rent	$ 27,000
Rantoul, Illinois
Commitments and contingencies
Lease expiration period description	Month to Month
Annual Rent	$ 36,000
Smyrna, Georgia
Commitments and contingencies
Lease Expiration Date	Jul. 01, 2030
Annual Rent	$ 492,000
Stony Point, New York
Commitments and contingencies
Lease Expiration Date	Jun. 01, 2023
Annual Rent	$ 118,000
Woodcliff Lake, New Jersey
Commitments and contingencies
Lease Expiration Date	Aug. 01, 2027
Annual Rent	$ 236,000