Retirement Benefits Accumulated Benefit Obligation (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Other Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation	$ 10,636	$ 11,454	$ 11,194
Defined Benefit Plan, Accumulated Benefit Obligation	10,557	11,367
Defined Benefit Plan, Plan Assets, Amount	5,960	7,138	$ 7,200
Fair Value, Measurements, Recurring | Level 1 | Other Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount
Fair Value, Measurements, Recurring | Level 1 | Mutual Funds | Qualified Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	103,661	117,796
Fair Value, Measurements, Recurring | Level 1 | Mutual Funds | Other Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,910	7,089
Fair Value, Measurements, Recurring | Level 1 | Cash and cash equivalents | Qualified Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	2,684
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Qualified Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	640,243	704,360
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Other Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,960	7,138
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Mutual Funds | Qualified Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	103,661	117,796
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Mutual Funds | Other Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	5,910	7,089
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Cash and cash equivalents | Qualified Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	702	11,988
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value Measurement [Domain] | Other Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	50	49
Fair Value, Measurements, Recurring | Level 2 | Other Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount
Fair Value, Measurements, Recurring | Level 2 | Mutual Funds | Qualified Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Level 2 | Mutual Funds | Other Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Measurements, Recurring | Level 2 | Cash and cash equivalents | Qualified Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 702	$ 9,304