Employee and Retiree Benefit Plans - Components of Net Periodic Benefit Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Recognized actuarial loss	$ (193)	$ 0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	7,964	8,994	$ 8,279
Interest cost	27,835	26,168	27,047
Expected return on plan assets	(25,719)	(29,236)	(28,941)
Amortization of prior service cost (credit)	964	1,021	1,026
Recognized actuarial loss	14,106	21,893	16,691
Net periodic benefit expense	25,150	28,840	24,102
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,559	1,965	1,601
Interest cost	3,864	3,427	3,444
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	0	(38)	(74)
Recognized actuarial loss			0
Net periodic benefit expense	$ 5,230	$ 5,354	$ 4,971