Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Change In Benefit Obligation [Line Items]
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation	$ 169,705	$ 158,580
Defined Benefit Plan, Amortization of Net Gains (Losses)	3,400
Defined Benefit Plan, Amortization of Net Prior Service Cost (Credit)	1,100
Defined Contribution Plan, Cost	14,200	9,900	$ 9,000
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Change In Benefit Obligation [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	19,308	15,614	13,098
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	14,500
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Change In Benefit Obligation [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	5,338	$ 6,347	$ 9,099
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 1,200
Debt Securities [Member]
Defined Benefit Plan Change In Benefit Obligation [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	40.00%
Equity Securities [Member]
Defined Benefit Plan Change In Benefit Obligation [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	60.00%