Retirement Plans - Summary of Categories in Fair Value Hierarchy (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2020
U.S. Corporate Bonds | Minimum
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, maturity period	10 years
Long-term Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, maturity period	10 years
Treasury Strips | Minimum
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, maturity period	20 years