Post Retirement Benefits - Multi-employer Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Multiemployer plans:
Pension Fund	cmt:InternationalAssociationofMachinistsAndAerospaceWorkersNationalPensionFundNationalPensionPlanMember
EIN	516031295
Pension Plan Number	002
Pension Protection Act Zone Status	Red	Red
FIP/RP Status Pending/Implemented	Implemented
Contributions of the Company	$ 676,000	$ 971,000	$ 760,000
Surcharge Imposed	Yes
Expiration Date of Collective Bargaining Agreement	Aug. 07, 2022