Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Components of Net Periodic Benefit Cost (Income) [Abstract]
Payment for pension benefits			$ 3,000
Expected future employer contributions, remainder of fiscal year	$ 10,200		10,200
Pension Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	2,322	$ 2,684	4,819	$ 5,888
Interest cost	6,615	6,102	13,244	12,210
Expected return on plan assets	(6,360)	(7,044)	(12,722)	(14,104)
Amortization of prior service cost (credit)	1,620	1	3,272	2
Recognized actuarial loss (gain)	0	1,108	0	2,180
Net Periodic Benefit Cost (Income)	4,197	2,851	8,613	6,176
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	77	87	166	199
Interest cost	150	142	305	289
Expected return on plan assets	(217)	(238)	(435)	(477)
Amortization of prior service cost (credit)	(470)	(470)	(941)	(941)
Recognized actuarial loss (gain)	(24)	(20)	(48)	(40)
Net Periodic Benefit Cost (Income)	$ (484)	$ (499)	$ (953)	$ (970)