Retirement Plans, Weighted Average Assumptions Used to Determine Net Periodic Benefit Cost, Pension Benefits (Details)		2 Months Ended		9 Months Ended	12 Months Ended
		Mar. 31, 2018	Feb. 14, 2018	Dec. 31, 2018	Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Weighted average assumptions used to determine net periodic benefit cost [Abstract]
Discount rate	[1]				3.50%		4.40%	3.70%
Expected long-term rate of return on plan assets					6.75%		7.00%	7.00%
Pension Benefits [Member] | Higman [Member]
Weighted average assumptions used to determine net periodic benefit cost [Abstract]
Discount rate		4.02%	4.13%	4.40%	3.10%	[1]
SERP [Member]
Weighted average assumptions used to determine net periodic benefit cost [Abstract]
Discount rate					3.50%		4.40%	3.70%
Expected long-term rate of return on plan assets					0.00%		0.00%	0.00%
Rate of compensation increase					0.00%		0.00%	0.00%

[1] The 2020 discount rate for benefit cost is 3.5% for the Kirby pension plan and 3.1% for the Higman pension plan. The 2018 discount rate for benefit cost for the Higman pension plan was changed from 4.13% as of February 14, 2018 and 4.02% as of March 31, 2018 to 4.40% as of December 31, 2018.