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, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of Net Periodic Pension Cost
Interest cost on projected benefit obligation	$ 3,456	$ 3,987	$ 3,882
Expected return on plan assets	(3,925)	(4,731)	(6,266)
Amortization of prior service credit - DNB merger	0	7	0
Recognized net actuarial loss	1,419	1,604	2,134
Settlement charge	833	0	0
Net Periodic Pension Expense	1,783	867	(250)
Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss)
Net actuarial loss/(gain)	(1,282)	2,370	(3,271)
Recognized net actuarial loss	(1,419)	(1,604)	(2,134)
Settlement loss recognized	(833)	0	0
Recognized prior service credit	0	0	0
Total (Before Tax Effects)	(3,534)	766	(5,405)
Total Recognized in Net Benefit Cost and Other Comprehensive Income/(Loss) (Before Tax Effects)	$ (1,751)	$ 1,633	$ (5,655)