Retirement Benefits - Fair Value Level 3 Rollforward (Details) - Fair Value, Measurements, Recurring - Net Receivables [Member] - Qualified Pension Benefits - Fair Value Measured at Net Asset Value Per Share [Member] $ in Thousands	Dec. 31, 2018 USD ($)
Change in plan assets:
Fair value of plan assets at beginning of period	$ 50,959
Fair value of plan assets at end of period	$ 1,345

Retirement Benefits - Fair Value Level 3 Rollforward (Details) - Fair Value, Measurements, Recurring - Net Receivables [Member] - Qualified Pension Benefits - Fair Value Measured at Net Asset Value Per Share [Member]
$ in Thousands

Dec. 31, 2018

USD ($)

Fair value of plan assets at beginning of period

$ 50,959

Fair value of plan assets at end of period

$ 1,345