Retirement Agreements and Other Postretirement Benefit Plan Effects on Net Periodic Postretirement Benefit Cost and Accumulated Postretirement Benefit Obligation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Retirement Benefits [Abstract]
One-Percent Point Increase: Effect on the service cost component	$ 0
One-Percent Point Increase: Effect on interest cost	6
One-Percent Point Increase: Total effect on the net periodic postretirement benefit cost	6
One-Percent Point Decrease: Effect on the service cost component	0
One-Percent Point Decrease: Effect on interest cost	(5)
One-Percent Point Decrease: Total effect on the net periodic postretirement benefit cost	(5)
One-Percent Point Increase: Effect on those currently receiving benefits (retirees and spouses)	0
One-Percent Point Increase: Effect on active fully eligible	191
One-Percent Point Increase: Effect on actives not yet eligible	0
One-Percent Point Increase: Total effect on the accumulated postretirement benefit obligation	191
One-Percent Point Decrease: Effect on those currently receiving benefits (retirees and spouses)	0
One-Percent Point Decrease: Effect on active fully eligible	(150)
One-Percent Point Decrease: Effect on actives not yet eligible	0
One-Percent Point Decrease: Total effect on the accumulated postretirement benefit obligation	$ (150)