Employee Benefit Plans Net Periodic Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Components of Net Periodic Benefit Cost
Service cost		$ 11,759	$ 12,362
Interest cost		26,210	26,174
Recognized actuarial loss		(7,006)	47,351
Settlements		0	0
Net Periodic Costs [Member] | Pension Plan [Member]
Components of Net Periodic Benefit Cost
Service cost		11,759	12,362	$ 10,830
Interest cost		26,210	26,174	26,147
Expected return on plan assets		(28,248)	(31,561)	(29,506)
Amortization of prior service cost (credit)		246	246	246
Recognized actuarial loss		9,888	10,634	2,118
Settlements		0	0	0
Net Periodic Benefit Cost (Credit)		19,855	17,855	9,835
Net Periodic Costs [Member] | Other Pension Plan, Postretirement or Supplemental Plans [Member]
Components of Net Periodic Benefit Cost
Service cost		492	526	465
Interest cost		795	786	859
Expected return on plan assets		(1,042)	(969)	(981)
Amortization of prior service cost (credit)		(1,882)	(1,882)	(1,998)
Recognized actuarial loss		315	385	348
Settlements		390	390	690
Net Periodic Benefit Cost (Credit)		$ (932)	$ (764)	$ (617)
Scenario, Forecast [Member] | Net Periodic Costs [Member] | Pension Plan [Member]
Components of Net Periodic Benefit Cost
Prior service credit (cost)	$ (9)
Scenario, Forecast [Member] | Net Periodic Costs [Member] | Other Pension Plan, Postretirement or Supplemental Plans [Member]
Components of Net Periodic Benefit Cost
Prior service credit (cost)	1,882
Scenario, Forecast [Member] | Pension Costs [Member] | Pension Plan [Member]
Components of Net Periodic Benefit Cost
Accumulated loss	(7,901)
Scenario, Forecast [Member] | Pension Costs [Member] | Other Pension Plan, Postretirement or Supplemental Plans [Member]
Components of Net Periodic Benefit Cost
Accumulated loss	$ (313)