Employee Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Pension Plan
Net periodic benefit cost
Service cost	$ 3,020	$ 2,707	$ 6,040	$ 5,414
Interest cost	1,728	2,066	3,456	4,132
Expected return on plan assets	(4,202)	(3,385)	(8,404)	(6,770)
Amortization of prior service credit	(809)	0	(1,618)	0
Amortization of net loss	999	979	1,998	1,958
Special event plan closure	0	0	0	0
Net periodic benefit cost	736	2,367	1,472	4,734
Estimated 2021 pension plan contribution, disclosed in prior year 10K					$ 10,000
Revised expected contribution	5,000		5,000
Contribution by employer			5,000
Postretirement Benefit Plan
Net periodic benefit cost
Service cost	0	432	148	864
Interest cost	1	253	70	506
Expected return on plan assets	0	0	0	0
Amortization of prior service credit	(3,765)	(2,021)	(6,962)	(4,042)
Amortization of net loss	705	94	1,197	188
Special event plan closure	0	0	(20,177)	0
Net periodic benefit cost	$ (3,059)	$ (1,242)	$ (25,724)	$ (2,484)