Employee Retirement Plans - Nonqualified Supplemental Defined Benefit and Postretirement Benefits (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Supplemental Employee Retirement Plan, Defined Benefit [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	[1]	$ 22,321		$ 19,366
Service Cost		1,235	[1]	1,490	[1]	$ 1,179
Interest Cost		699	[1]	654	[1]	600
Actuarial loss	[1]	1,874		831
Benefits paid	[1]	(6)		(5)
Settlements	[1]	0		(15)
Benefit obligation at end of year	[1]	26,123		22,321		19,366
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		0		0
Employer contribution		6		20
Benefits paid		(6)		(5)
Settlements		0		(15)
Fair value of plan assets at end of year		0		0		0
Funded status at end of year		(26,123)		(22,321)
Other Postretirement Benefit Plan, Defined Benefit [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	[1]	955		1,056
Service Cost		38	[1]	45	[1]	38
Interest Cost		42	[1]	37	[1]	36
Actuarial loss	[1]	321		(161)
Benefits paid	[1]	(17)		(22)
Settlements	[1]	0		0
Benefit obligation at end of year	[1]	1,339		955		1,056
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		0		0
Employer contribution		17		22
Benefits paid		(17)		(22)
Settlements		0		0
Fair value of plan assets at end of year		0		0		$ 0
Funded status at end of year		$ (1,339)		$ (955)

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