Employee Benefit Plans (Summary of Net Periodic Benefit Cost) (Details) - Employee Pension Plans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of net periodic benefit cost
Interest cost	$ 3,032	$ 3,801	$ 3,496
Service cost	925	900	875
Expected return on plan assets	(4,022)	(4,170)	(4,302)
Recognized net actuarial losses	2,407	1,933	2,067
Net periodic benefit cost	$ 2,342	$ 2,464	$ 2,136
Actuarial assumptions used to determine net cost:
Discount rate (as a percent)	3.07%	4.12%	3.45%
Expected return on assets (as a percent)	5.75%	5.75%	6.00%