Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - Supplemental Retirement Plan [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net periodic benefit cost [Abstract]
Service cost	$ 20	$ 28	$ 39	$ 55
Interest cost	387	501	801	1,042
Amortization of prior service cost	38	62	75	125
Recognized net actuarial loss	236	154	482	316
Net periodic benefit cost	$ 681	$ 745	$ 1,397	$ 1,538