Leases - Summary of Amounts Included in the Condensed Consolidated Statement of Financial Position (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Operating lease assets	$ 20,820	$ 18,390
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	mye:RightOfUseAssetOperatingLeasesMember	mye:RightOfUseAssetOperatingLeasesMember
Finance lease assets	$ 10,282
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentMember	us-gaap:PropertyPlantAndEquipmentMember
Total lease assets	$ 31,102	$ 18,390
Liabilities:
Current	$ 4,269	$ 4,359
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	mye:OperatingLeaseLiabilityShortTermMember	mye:OperatingLeaseLiabilityShortTermMember
Long-term	$ 16,300	$ 13,755
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	mye:OperatingLeaseLiabilityLongTermMember	mye:OperatingLeaseLiabilityLongTermMember
Total operating lease liabilities	$ 20,569	$ 18,114
Current	$ 487	$ 0
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	mye:FinanceLeaseLiabilityShortTermMember	mye:FinanceLeaseLiabilityShortTermMember
Long-term	$ 9,812	$ 0
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	mye:FinanceLeaseLiabilityLongTermMember	mye:FinanceLeaseLiabilityLongTermMember
Total finance lease liabilities	$ 10,299
Total lease liabilities	$ 30,868	$ 18,114