Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined contribution plan, cost recognized	$ 11,100	$ 8,600	$ 10,700
Salary continuation plan minimum period	10 years
Salary continuation plan maximum period	20 years
Present value of future salary contribution plan benefits	$ 28,900	28,700
Postemployment benefits, period expense	3,600	1,500	$ 1,000
Deferred compensation cash-based arrangements, liability, current and noncurrent	12,800	12,200
Cash surrender value of life insurance	323,500	320,600
Other postretirement defined benefit plan, liabilities	3,700	3,400
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other deferred compensation arrangements, liability, current and noncurrent	$ 559	529
Percentage of deferred salary	50.00%
Deferred compensation liability, current and noncurrent	$ 10,300	9,700
Pension and other postretirement defined benefit plans, liabilities	$ 9,100	$ 9,000