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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net periodic benefit cost [Abstract]
Service cost	$ 27	$ 29	$ 82	$ 87
Interest cost	502	457	1,544	1,409
Amortization of prior service cost	62	63	187	188
Recognized net actuarial loss	155	218	471	664
Net periodic benefit cost	$ 746	$ 767	$ 2,284	$ 2,348