| **Employee Benefit Plans (Details) $ in Thousands**         |        | 3 Months Ended | 9 Months Ended |
|-------------------------------------------------------------|--------|----------------|----------------|
||
| **Components of net periodic cost (benefit):**              |   |           |           |   |   |
| Service cost                                                |   | $ 3,839        | $ 1,845        | $ 7,241 | $ 5,530 |
| Interest cost                                               |   | 7,012          | 6,694          | 20,814 | 20,002 |
| Expected return on plan assets                              |   | (6,237)        | (7,084)        | (18,793) | (21,258) |
| Amortization of unrecognized prior service costs (benefits) |   | (150)          | (159)          | (452) | (520) |
| Amortization of losses (gains) from earlier periods         |   | 2,644          | 3,268          | 7,414 | 9,497 |
| Net periodic cost (benefit)                                 |   | 7,108          | 4,564          | 16,224 | 13,251 |
| Defined Benefit Pension Plan                                |   |           |           |   |   |
| **Components of net periodic cost (benefit):**              |   |           |           |   |   |
| Service cost                                                |   | 3,417          | 1,521          | 6,087 | 4,538 |
| Interest cost                                               |   | 6,384          | 5,996          | 18,948 | 17,990 |
| Expected return on plan assets                              |   | (6,237)        | (7,084)        | (18,793) | (21,258) |
| Amortization of unrecognized prior service costs (benefits) |   | 0              | 3              | 0 | 10 |
| Amortization of losses (gains) from earlier periods         |   | 2,726          | 3,086          | 7,695 | 9,298 |
| Net periodic cost (benefit)                                 |   | 6,290          | 3,522          | 13,937 | 10,578 |
| Expected Employer contribution for the year                 |   |           |           | 0 |   |
| Post-Retirement Medical Plan                                |   |           |           |   |   |
| **Components of net periodic cost (benefit):**              |   |           |           |   |   |
| Service cost                                                |   | 349            | 254            | 935 | 781 |
| Interest cost                                               |   | 184            | 167            | 534 | 420 |
| Expected return on plan assets                              |   | 0              | 0              | 0 | 0 |
| Amortization of unrecognized prior service costs (benefits) |   | (275)          | (395)          | (827) | (1,230) |
| Amortization of losses (gains) from earlier periods         |   | (67)           | 16             | (237) | (298) |
| Net periodic cost (benefit)                                 |   | 191            | 42             | 405 | (327) |
| Expected Employer contribution for the year                 |   |           |           | 803 |   |
| Payments to plan                                            |   | 212            | 576            | 603 | 1,100 |
| Post-Retirement Medical Plan | Putnam                       |   |           |           |   |   |
| **Components of net periodic cost (benefit):**              |   |           |           |   |   |
| Number of individuals | plan_participant                    | 150    |           |           |   |   |
| Post-Retirement Medical Plan | Other Liabilities | Putnam   |   |           |           |   |   |
| **Components of net periodic cost (benefit):**              |   |           |           |   |   |
| Prior service cost                                          | $ 339  |           |           |   |   |
| Supplemental Executive Retirement Plan                      |   |           |           |   |   |
| **Components of net periodic cost (benefit):**              |   |           |           |   |   |
| Service cost                                                |   | 73             | 70             | 219 | 211 |
| Interest cost                                               |   | 444            | 531            | 1,332 | 1,592 |
| Expected return on plan assets                              |   | 0              | 0              | 0 | 0 |
| Amortization of unrecognized prior service costs (benefits) |   | 125            | 233            | 375 | 700 |
| Amortization of losses (gains) from earlier periods         |   | (15)           | 166            | (44) | 497 |
| Net periodic cost (benefit)                                 |   | 627            | 1,000          | 1,882 | 3,000 |
| Expected Employer contribution for the year                 |   |           |           | 3,336 |   |
| Payments to plan                                            |   | $ 834          | $ 830          | $ 2,502 | $ 3,995 |

| X                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined Benefit Plan, Number of Employees Covered
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of gains or losses recognized in net periodic benefit cost.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Net increase or decrease in the plan benefit obligation during the reporting period.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The increase in the fair value of plan assets from contributions made by the employer.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.
+ References
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