Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Components of Net Periodic Benefit Cost (Income) [Abstract]
Payment for pension benefits			$ 4,800
Minimum Expected Future Employer Pension Contributions, Remainder of Fiscal Year	$ 6,600		6,600
Pension Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	2,712	$ 2,322	5,558	$ 4,819
Interest cost	5,694	6,615	11,420	13,244
Expected return on plan assets	(6,536)	(6,360)	(13,081)	(12,722)
Amortization of prior service cost (credit)	0	1,620	0	3,272
Recognized actuarial loss (gain)	1,234	0	2,514	0
Net periodic benefit cost (credit)	3,104	4,197	6,411	8,613
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	93	77	185	166
Interest cost	137	150	246	305
Expected return on plan assets	(245)	(217)	(492)	(435)
Amortization of prior service cost (credit)	(470)	(470)	(941)	(941)
Recognized actuarial loss (gain)	(12)	(24)	(30)	(48)
Net periodic benefit cost (credit)	$ (497)	$ (484)	$ (1,032)	$ (953)