Pension and Postretirement Benefits - Composition of Net Periodic Pension Plan and Postretirement Plan Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 124	$ 119	$ 371	$ 355
Expected return on plan assets	(234)	(260)	(701)	(778)
Amortization of net losses	82	41	246	123
Net periodic benefit plan (benefit) cost	(28)	(100)	(84)	(300)
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	6	5	16	16
Amortization of prior service credits	(1)	(1)	(3)	(3)
Amortization of net losses	3	3	9	9
Net periodic benefit plan (benefit) cost	$ 8	$ 7	$ 22	$ 22