Employee's Pension and Postretirement Benefits - Amounts Accrued and Unfunded Status (Details) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Amounts Accrued
Obligation, beginning of period	$ 20,116	$ 18,840
Interest cost	18	379
Actuarial gain	0	897
Obligation, end of period and unfunded status	$ 20,134	$ 20,116