Employees Retirement Plans - Components of net periodic benefit cost and other amounts recognized in AOCL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Total amount recognized in other comprehensive income	$ 1,531		$ (679)		$ (184)
Supplemental Employee Retirement Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	1,235	[1]	1,490	[1]	1,179
Interest Cost	699	[1]	654	[1]	600
Amortization of prior service cost	86		86		86
Amortization of net actuarial loss	571		1,248		676
Net periodic benefit cost	2,591		3,478		2,541
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Amortization of prior service cost	(86)		(86)		(86)
Amortization of net actuarial loss	(571)		(1,248)		(676)
Net actuarial loss (gain)	1,874		831		459
Total amount recognized in other comprehensive income	1,217		(503)		(303)
Total amount recognized in net periodic benefit cost and other comprehensive income	3,808		2,975		2,238
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	38	[1]	45	[1]	38
Interest Cost	42	[1]	37	[1]	36
Amortization of prior service cost	0		0		0
Amortization of net actuarial loss	7		15		8
Net periodic benefit cost	87		97		82
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Amortization of prior service cost	0		0		0
Amortization of net actuarial loss	(7)		(15)		(8)
Net actuarial loss (gain)	321		(161)		127
Total amount recognized in other comprehensive income	314		(176)		119
Total amount recognized in net periodic benefit cost and other comprehensive income	$ 401		$ (79)		$ 201

[1] Represents the projected benefit obligation for the nonqualified supplemental defined benefit retirement plan and the accumulated postretirement benefit obligation for postretirement benefits.