Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Components of net periodic benefit cost (income)
Service cost	$ 2,262	$ 2,217	$ 6,384	$ 6,919
Interest cost	2,644	2,950	8,432	8,897
Expected return on plan assets	(3,123)	(3,006)	(9,679)	(9,483)
Settlement expense	2,122	4,611	3,897	5,083
Curtailment income	0	(40)	0	(40)
Amortization of net loss (gain)	513	329	914	1,581
Amortization of prior service cost (credit)	94	44	186	131
Net periodic benefit cost (income)	4,512	7,105	10,134	13,088
Postretirement Benefits
Components of net periodic benefit cost (income)
Service cost	143	164	430	493
Interest cost	140	123	418	368
Expected return on plan assets	0	0	0	0
Settlement expense	0	0	0	0
Curtailment income	0	0	0	0
Amortization of net loss (gain)	(359)	(385)	(1,077)	(1,155)
Amortization of prior service cost (credit)	(35)	(35)	(103)	(103)
Net periodic benefit cost (income)	$ (111)	$ (133)	$ (332)	$ (397)