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Employee Benefit Plans - Schedule of Funded Status of Benefit Obligation and Plan Assets (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Change in benefit obligation: |  |  |  |
Interest cost |  | $ 83 | $ 89 | $ 91
Change in plan assets: |  |  |  |
Balance, beginning of year |  | 57,746 |  |
Balance, end of year |  | 52,250 | 57,746 |
Chesapeake Pension Plan |  |  |  |
Change in benefit obligation: |  |  |  |
Benefit obligation - beginning of year |  | 11,443 | 11,355 |
Interest cost |  | 384 | 402 | 421
Actuarial loss |  | (610) | 454 |
Benefits paid |  | (505) | (768) |
Benefit obligation - end of year |  | 10,712 | 11,443 | 11,355
Change in plan assets: |  |  |  |
Balance, beginning of year |  | 9,350 | 8,668 |
Actual return on plan assets |  | (647) | 1,144 |
Employer contributions |  | 451 | 306 |
Benefits paid |  | (505) | (768) |
Balance, end of year |  | 8,649 | 9,350 | $ 8,668
Reconciliation: |  |  |  |
Funded status |  | (2,063) | (2,093) |
Accrued pension cost |  | $ (2,063) | $ (2,093) |
Assumptions: |  |  |  |
Discount rate |  | 4.00% | 3.50% |
Expected return on plan assets |  | 6.00% | 6.00% | 6.00%
FPU Pension Plan |  |  |  |
Change in benefit obligation: |  |  |  |
Benefit obligation - beginning of year |  | $ 64,664 | $ 63,832 |
Interest cost |  | 2,339 | 2,482 | $ 2,525
Actuarial loss |  | (4,739) | 1,199 |
Benefits paid |  | (2,887) | (2,849) |
Benefit obligation - end of year |  | 59,377 | 64,664 | 63,832
Change in plan assets: |  |  |  |
Balance, beginning of year |  | 48,396 | 43,272 |
Actual return on plan assets |  | (3,113) | 6,025 |
Employer contributions |  | 1,205 | 1,948 |
Benefits paid |  | (2,887) | (2,849) |
Balance, end of year |  | 43,601 | 48,396 | $ 43,272
Reconciliation: |  |  |  |
Funded status |  | (15,776) | (16,268) |
Accrued pension cost |  | $ (15,776) | $ (16,268) |
Assumptions: |  |  |  |
Discount rate |  | 4.25% | 3.75% |
Expected return on plan assets |  | 6.50% | 6.50% | 6.50%
Chesapeake SERP |  |  |  |
Change in benefit obligation: |  |  |  |
Benefit obligation - beginning of year |  | $ 2,428 | $ 2,428 |
Interest cost |  | 83 | 89 |
Actuarial loss |  | (74) | 63 |
Benefits paid |  | (152) | (152) |
Benefit obligation - end of year |  | 2,285 | 2,428 | $ 2,428
Change in plan assets: |  |  |  |
Employer contributions |  | 152 | 152 |
Benefits paid |  | (152) | (152) |
Reconciliation: |  |  |  |
Funded status |  | (2,285) | (2,428) |
Accrued pension cost |  | $ (2,285) | $ (2,428) |
Assumptions: |  |  |  |
Discount rate |  | 4.00% | 3.50% |
Chesapeake Postretirement Plan |  |  |  |
Change in benefit obligation: |  |  |  |
Benefit obligation - beginning of year |  | $ 1,128 | $ 1,132 |
Interest cost |  | 38 | 41 | 43
Plan participants contributions |  | 136 | 118 |
Actuarial loss |  | (131) | 72 |
Benefits paid |  | (169) | (235) |
Benefit obligation - end of year |  | 1,002 | 1,128 | 1,132
Change in plan assets: |  |  |  |
Balance, beginning of year |  | 0 | 0 |
Employer contributions | [1] | 33 | 117 |
Plan participants contributions |  | 136 | 118 |
Benefits paid |  | (169) | (235) |
Balance, end of year |  | 0 | 0 | 0
Reconciliation: |  |  |  |
Funded status |  | (1,002) | (1,128) |
Accrued pension cost |  | $ (1,002) | $ (1,128) |
Assumptions: |  |  |  |
Discount rate |  | 4.00% | 3.50% |
FPU Medical Plan |  |  |  |
Change in benefit obligation: |  |  |  |
Benefit obligation - beginning of year |  | $ 1,287 | $ 1,349 |
Interest cost |  | 47 | 50 | 55
Plan participants contributions |  | 41 | 48 |
Actuarial loss |  | (89) | (48) |
Benefits paid |  | (99) | (112) |
Benefit obligation - end of year |  | 1,187 | 1,287 | 1,349
Change in plan assets: |  |  |  |
Balance, beginning of year |  | 0 | 0 |
Employer contributions | [1] | 58 | 64 |
Plan participants contributions |  | 41 | 48 |
Benefits paid |  | (99) | (112) |
Balance, end of year |  | 0 | 0 | $ 0
Reconciliation: |  |  |  |
Funded status |  | (1,187) | (1,287) |
Accrued pension cost |  | $ (1,187) | $ (1,287) |
Assumptions: |  |  |  |
Discount rate |  | 4.25% | 3.75% |
[1] | The Chesapeake Postretirement Plan does not receive a Medicare Part-D subsidy. The FPU Medical Plan did not receive a significant subsidy for the post-merger period.

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- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 + Details
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- Definition Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(6) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964 + Details
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