Employee Benefit Plans Net Periodic Costs (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan [Member]
Components of Net Periodic Benefit Cost
Service cost		$ 9,637	$ 11,776
Interest cost		26,488	24,420
Recognized actuarial loss (gain)		(83,364)	53,496
Settlements		(4,065)	0
Net Periodic Costs [Member] | Pension Plan [Member]
Components of Net Periodic Benefit Cost
Service cost		9,637	11,776	$ 10,994
Interest cost		26,488	24,420	25,633
Expected return on plan assets		(25,443)	(28,207)	(23,964)
Amortization of prior service cost (credit)		0	4	4
Recognized actuarial loss (gain)		6,544	4,360	7,837
Settlements		198	0	0
Net Periodic Benefit Cost (Credit)		17,424	12,353	20,504
Regulatory deferral of net periodic benefit cost (1)	[1]	(7,510)	(4,057)	(11,751)
Previously deferred costs recognized (1)	[1]	728	243	724
Amount Recognized in Income		10,642	8,539	9,477
Operating, general and administrative expense		2,125	7,719	(757)
Other income (expense), net		8,517	820	10,234
Amount Recognized in Income		10,642	8,539	9,477
Net Periodic Costs [Member] | Other Pension, Postretirement and Supplemental Plans [Member]
Components of Net Periodic Benefit Cost
Service cost		331	398	456
Interest cost		609	578	715
Expected return on plan assets		(869)	(954)	(846)
Amortization of prior service cost (credit)		(1,882)	(1,882)	(1,882)
Recognized actuarial loss (gain)		(96)	(79)	318
Settlements		390	390	390
Net Periodic Benefit Cost (Credit)		(1,517)	(1,549)	(849)
Regulatory deferral of net periodic benefit cost (1)	[1]	0	0	0
Previously deferred costs recognized (1)	[1]	931	913	1,153
Amount Recognized in Income		(586)	(636)	304
Operating, general and administrative expense		331	398	457
Other income (expense), net		(917)	(1,034)	(153)
Amount Recognized in Income		$ (586)	$ (636)	$ 304

[1] Net periodic benefit costs for pension and postretirement benefit plans are recognized for financial reporting based on the authorization of each regulatory jurisdiction in which we operate. A portion of these costs are recorded in regulatory assets and recognized in the Consolidated Statements of Income as those costs are recovered through customer rates.