Leases - Summary of Amounts Included in the Condensed Consolidated Statement of Financial Position (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Assets:
Operating lease assets	$ 30,532	$ 18,390
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	mye:RightOfUseAssetOperatingLeasesMember	mye:RightOfUseAssetOperatingLeasesMember
Finance lease assets	$ 9,937
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentMember	us-gaap:PropertyPlantAndEquipmentMember
Total lease assets	$ 40,469	$ 18,390
Liabilities:
Current	$ 5,369	$ 4,359
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	mye:OperatingLeaseLiabilityShortTermMember	mye:OperatingLeaseLiabilityShortTermMember
Long-term	$ 24,989	$ 13,755
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	mye:OperatingLeaseLiabilityLongTermMember	mye:OperatingLeaseLiabilityLongTermMember
Total operating lease liabilities	$ 30,358	$ 18,114
Current	$ 495	$ 0
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	mye:FinanceLeaseLiabilityShortTermMember	mye:FinanceLeaseLiabilityShortTermMember
Long-term	$ 9,563	$ 0
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	mye:FinanceLeaseLiabilityLongTermMember	mye:FinanceLeaseLiabilityLongTermMember
Total finance lease liabilities	$ 10,058
Total lease liabilities	$ 40,416	$ 18,114