Defined Benefit and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - Supplemental Retirement Plan [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net periodic benefit cost [Abstract]
Service cost	$ 19	$ 27	$ 58	$ 82
Interest cost	388	502	1,189	1,544
Amortization of prior service cost	37	62	112	187
Recognized net actuarial loss	237	155	719	471
Net periodic benefit cost	$ 681	$ 746	$ 2,078	$ 2,284