Employee Benefit Plan - Pension Plan Weighted-Average Asset Allocations (Details) - DB Pension Plan |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Defined Contribution Plan Disclosure [Line Items] | ||
| Weighted-average asset allocations | 100.00% | 100.00% |
| Equity securities | ||
| Defined Contribution Plan Disclosure [Line Items] | ||
| Weighted-average asset allocations | 65.00% | 68.00% |
| Debt securities | ||
| Defined Contribution Plan Disclosure [Line Items] | ||
| Weighted-average asset allocations | 34.00% | 30.00% |
| Other | ||
| Defined Contribution Plan Disclosure [Line Items] | ||
| Weighted-average asset allocations | 1.00% | 2.00% |