Postretirement Benefits Other than Pensions - Change in Benefit Obligation (Details) - Postretirement Health Coverage [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 2,774	$ 3,167
Interest cost	101	96	$ 108
Actuarial (gain) loss	196	(96)
Benefits paid	(336)	(393)
Benefit obligation at end of year	$ 2,735	$ 2,774	$ 3,167