Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of Net Periodic Pension Cost
Interest cost on projected benefit obligation	$ 3,987	$ 3,882	$ 4,100
Expected return on plan assets	(4,731)	(6,266)	(6,313)
Amortization of prior service credit - DNB merger	7	0	0
Recognized net actuarial loss	1,604	2,134	1,866
Net Periodic Pension Expense	867	(250)	(347)
Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss)
Net actuarial loss/(gain)	2,370	(3,271)	3,678
Recognized net actuarial loss	(1,604)	(2,134)	(1,866)
Recognized prior service credit	0	0	0
Total (Before Tax Effects)	766	(5,405)	1,812
Total Recognized in Net Benefit Cost and Other Comprehensive Income/(Loss) (Before Tax Effects)	$ 1,633	$ (5,655)	$ 1,465