Pension and Other Postretirement Benefit Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Term of insurance contracts to fund benefits		5 years
Curtailment	$ 1,049,000	$ 2,621,000	$ 1,219,000
Contributions by employer	$ 601,000	$ 1,558,000	$ 0
Assumptions used calculating benefit obligation, discount rate	0.45%	1.05%