Pensions and Other Employee Benefits Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Unfunded status at end of period	$ (20,300)
Unfunded benefit obligations, discount rate	2.50%	3.25%
Unfunded benefit obligations, decrease in discount rate		0.50%
Change in unfunded benefit obligation as a result of decrease in half percentage point assumed discount rate	$ 4,400	$ 3,700
Accumulated pension benefit obligation	$ 60,300	54,200
Expected long-term rate of return on plan assets for 2021	6.75%
Defined benefit plan, target allocation percentage	The target allocation within the liquid return-seeking portfolio is 75% global equities, 15% marketable real assets and 10% fixed income. Allocations may vary by up to 5% from these targets
Employee Savings (401K) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions to employee savings (401K) plan, maximum	6.00%
Participant's base salary rate	66.70%
Employer contributions	$ 100	100
Liquid Return Seeking [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation variance percentage	5.00%
Liquid Return Seeking [Member] | Global Equities[Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage	75%
Liquid Return Seeking [Member] | Marketable Real Assets[Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage	15%
Liquid Return Seeking [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation percentage	10%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain) component of benefit obligation	$ (5,453)	(5,256)
Contribution to qualified pension plan	1,953	942
Estimated employer contribution next fiscal year	1,300
Pension Benefits [Member] | Change in Discount Rate [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain) component of benefit obligation	(5,800)	6,700
Pension Benefits [Member] | Other Factors [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain) component of benefit obligation	300	1,400
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain) component of benefit obligation	(30)	(30)
Contribution to qualified pension plan	$ 19	$ 19