Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost		$ 1,356	$ 1,491	$ 4,064	$ 4,479
Interest cost		4,539	4,336	13,647	13,028
Expected return on plan assets		(7,389)	(7,615)	(21,816)	(22,392)
Amortization of prior service cost (credit)		101	141	302	422
Amortization of actuarial (gains) losses		2,215	2,879	6,658	8,719
Settlement loss		93	0	340	0
Net periodic benefit cost		915	1,232	3,195	4,256
Pensions [Member] | Qualified Plan [Member]
Pension and other postretirement benefits expenses
Discretionary contributions	$ 15,000
Pensions [Member] | Nonqualified Plan [Member]
Pension and other postretirement benefits expenses
Expected company contributions		5,000		5,000
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost		18	22	53	64
Interest cost		335	338	1,008	1,019
Amortization of prior service cost (credit)		6	5	19	15
Amortization of actuarial (gains) losses		3	135	10	421
Net periodic benefit cost		$ 362	$ 500	$ 1,090	$ 1,519