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Employee Benefits - Additional Information (Details) |  |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Sep. 07, 2018 USD ($) | Dec. 19, 2017 USD ($) retiree | Dec. 31, 2017 USD ($) | Dec. 31, 2019 USD ($) transfer | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Number of consecutive years of employee's compensation |  |  |  | 5 years |  |
Number of total years of employee's compensation |  |  |  | 10 years |  |
Service cost |  |  |  | $ 0 |  |
Expected long-term rate of return on plan assets |  |  |  | 4.80% | 7.50% | 7.50%
Employer contributions | $ 20,400,000 |  |  | $ 0 | $ 20,420,000 |
Return to provision discrete tax benefit |  |  | $ 2,900,000 |  |  |
Net actuarial loss included in accumulated other comprehensive losses expected to be recognized |  |  |  | 1,500,000 |  |
Future prior service credit to be recognized due to freeze of accrual benefits |  |  |  | 0 |  |
Accumulated benefit obligation |  |  |  | 113,700,000 | 95,200,000 |
Number of retirees covered by annuity contract | retiree |  | 124 |  |  |  |
Number of retirees covered by annuity contract receiving death benefits | retiree |  | 30 |  |  |  |
Defined benefit obligations, death benefits |  | $ 2,000 |  |  |  |
Total premium paid out of plan's assets |  | $ 1,500,000 |  | 6,282,000 | 7,975,000 |
Projected benefit obligation |  |  | 106,664,000 | 113,679,000 | 95,200,000 | $ 106,664,000
Net periodic benefit cost |  |  |  | $ 867,000 | (250,000) | (347,000)
Transfers of plan assets between levels 1 and 2 on recurring basis |  |  |  |  | 2,200,000 |
Number of transfers | transfer |  |  |  | 0 |  |
Purchases of level 3 plan assets |  |  |  | $ 0 | 0 |
Transfers of level 3 plan assets |  |  |  | 0 | 0 |
Required cash contributions to the plan |  |  |  | 100,000 |  |
Supplemental Executive Retirement Plan |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Projected benefit obligation |  |  |  | 5,300,000 | 4,400,000 |
Net periodic benefit cost |  |  |  | 400,000 | 500,000 | 500,000
Amounts before tax reflected in accumulated other comprehensive income (loss) |  |  | $ 2,700,000 | $ 2,400,000 | 1,900,000 | 2,700,000
Thrift Plan |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Contributions to the Thrift Plan |  |  |  | 3.50% |  |
Compensation expense |  |  |  | $ 2,000,000.0 | $ 1,700,000 | $ 1,800,000
Total equity securities | Minimum |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Targeted asset allocation percentage |  |  |  | 5.00% | 50.00% |
Total equity securities | Maximum |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Targeted asset allocation percentage |  |  |  | 15.00% | 70.00% |
Fixed income | Minimum |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Targeted asset allocation percentage |  |  |  | 85.00% | 30.00% |
Fixed income | Maximum |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Targeted asset allocation percentage |  |  |  | 95.00% | 50.00% |

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