Pension Plans, Noncontributory Supplemental Pension Plan (Details) - USD ($) $ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Defined Benefit Plan Disclosure [Line Items] | ||
| Pension liability | $ 30,892 | $ 62,945 |
| Noncontributory Supplemental Pension Plan [Member] | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Pension liability | 7,413 | 8,224 |
| Accumulated other comprehensive loss related to noncontributory pension plan, net of tax | 107 | 862 |
| Accumulated other comprehensive loss related to noncontributory pension plan, tax | $ 73 | $ 556 |