Employee Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Pension Plan
Net periodic benefit cost
Service cost	$ 3,020	$ 2,707
Interest cost	1,728	2,066
Expected return on plan assets	(4,202)	(3,385)
Amortization of prior service credit	(809)	0
Amortization of net loss	999	979
Special event plan closure	0	0
Net periodic benefit cost	736	2,367
Postretirement Benefit Plan
Net periodic benefit cost
Service cost	148	432
Interest cost	69	253
Expected return on plan assets	0	0
Amortization of prior service credit	(3,196)	(2,021)
Amortization of net loss	492	94
Special event plan closure	(20,177)	0
Net periodic benefit cost	(22,664)	$ (1,242)
Estimated 2021 pension plan contribution, disclosed in prior year 10K			$ 10,000
Contribution by employer	$ 2,500