Pension and Retirement Plans - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Plan
Net periodic benefit cost
Interest cost	$ 414	$ 392	$ 840	$ 778
Expected return on assets	(651)	(722)	(1,360)	(1,445)
Amortization of prior service cost (credit)	(1)	(1)	(2)	(2)
Amortization of net actuarial loss	77	37	77	53
Net periodic benefit cost (credit)	(161)	(294)	(445)	(616)
Supplemental Retirement Plan
Net periodic benefit cost
Service cost	75	88	143	177
Interest cost	85	77	175	154
Amortization of net actuarial loss		1		2
Net periodic benefit cost (credit)	160	166	318	333
Postretirement Healthcare Plan
Net periodic benefit cost
Service cost	5	5	10	11
Interest cost	6	6	12	11
Amortization of net actuarial loss	(1)	(5)	(2)
Net periodic benefit cost (credit)	$ 10	$ 6	$ 20	$ 22