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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net periodic benefit cost [Abstract]
Service cost	$ 28	$ 29	$ 55	$ 58
Interest cost	501	457	1,042	952
Amortization of prior service cost	62	62	125	125
Recognized net actuarial loss	154	220	316	446
Net periodic benefit cost	$ 745	$ 768	$ 1,538	$ 1,581