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Employee Benefit Plans - Component of Net Periodic Pension Cost (Benefit) (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Components of net periodic cost: |  |  |  |
Interest cost |  | $ 83 | $ 89 | $ 91
Expected Amortization Of Pre Merger Regulatory Asset |  | 0 |  |
Assumptions |  |  |  |
Defined Benefit Plan, Plan Assets, Amount |  | 52,250 | 57,746 |
Chesapeake Postretirement Plan |  |  |  |
Components of net periodic cost: |  |  |  |
Interest cost |  | 38 | 41 | 43
Amortization of prior service cost |  | (77) | (77) | (77)
Actuarial (gain) loss |  | 58 | 53 | 64
Net periodic pension cost |  | 19 | 17 | 30
Expected Amortization Of Pre Merger Regulatory Asset |  |  | 0 | 0
Net periodic postretirement cost | [1] | $ 19 | $ 17 | $ 30
Assumptions |  |  |  |
Discount rate |  | 3.50% | 3.75% | 3.75%
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  | $ 136 | $ 118 |
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) |  | (131) | 72 |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  | (169) | (235) |
Defined Benefit Plan, Plan Assets, Amount |  | 0 | 0 | $ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer | [2] | 33 | 117 |
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant |  | 136 | 118 |
Defined Benefit Plan, Plan Assets, Benefits Paid |  | (169) | (235) |
Funded status |  | (1,002) | (1,128) |
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits |  | $ 1,002 | $ 1,128 |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 4.00% | 3.50% |
FPU Medical Plan |  |  |  |
Components of net periodic cost: |  |  |  |
Interest cost |  | $ 47 | $ 50 | 55
Amortization of prior service cost |  | 0 | 0 | 0
Actuarial (gain) loss |  | 0 | 0 | 0
Net periodic pension cost |  | 47 | 50 | 55
Amortization of pre-merger regulatory asset |  | 8 | 8 | 8
Net periodic postretirement cost | [1] | $ 55 | $ 58 | $ 63
Assumptions |  |  |  |
Discount rate |  | 3.75% | 4.00% | 4.00%
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  | $ 41 | $ 48 |
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) |  | (89) | (48) |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  | (99) | (112) |
Defined Benefit Plan, Plan Assets, Amount |  | 0 | 0 | $ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer | [2] | 58 | 64 |
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant |  | 41 | 48 |
Defined Benefit Plan, Plan Assets, Benefits Paid |  | (99) | (112) |
Funded status |  | (1,187) | (1,287) |
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits |  | $ 1,187 | $ 1,287 |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 4.25% | 3.75% |
Chesapeake SERP |  |  |  |
Components of net periodic cost: |  |  |  |
Interest cost |  | $ 83 | $ 89 |
Actuarial (gain) loss |  | 101 | 87 | 87
Net periodic postretirement cost |  | $ 184 | $ 176 | $ 178
Assumptions |  |  |  |
Discount rate |  | 3.50% | 3.75% | 3.75%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) |  | $ (74) | $ 63 |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  | (152) | (152) |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  | 152 | 152 |
Defined Benefit Plan, Plan Assets, Benefits Paid |  | (152) | (152) |
Funded status |  | (2,285) | (2,428) |
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits |  | $ 2,285 | $ 2,428 |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 4.00% | 3.50% |
Chesapeake Pension Plan |  |  |  |
Components of net periodic cost: |  |  |  |
Interest cost |  | $ 384 | $ 402 | $ 421
Expected return on assets |  | (542) | (495) | (501)
Actuarial (gain) loss |  | 343 | 399 | 459
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement |  | 0 | 0 | 161
Net periodic pension cost |  | 185 | 306 | 540
Amortization of pre-merger regulatory asset |  | 0 | 0 | 0
Net periodic postretirement cost |  | $ 185 | $ 306 | $ 540
Assumptions |  |  |  |
Discount rate |  | 3.50% | 3.75% | 3.75%
Expected return on plan assets |  | 6.00% | 6.00% | 6.00%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) |  | $ (610) | $ 454 |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  | (505) | (768) |
Defined Benefit Plan, Plan Assets, Amount |  | 8,649 | 9,350 | $ 8,668
Defined Benefit Plan, Plan Assets, Contributions by Employer |  | 451 | 306 |
Defined Benefit Plan, Plan Assets, Benefits Paid |  | (505) | (768) |
Funded status |  | (2,063) | (2,093) |
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits |  | $ 2,063 | $ 2,093 |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 4.00% | 3.50% |
FPU Pension Plan |  |  |  |
Components of net periodic cost: |  |  |  |
Interest cost |  | $ 2,339 | $ 2,482 | 2,525
Expected return on assets |  | (3,091) | (2,779) | (2,702)
Actuarial (gain) loss |  | 404 | 513 | 519
Net periodic pension cost |  | (348) | 216 | 342
Amortization of pre-merger regulatory asset |  | 761 | 761 | 761
Net periodic postretirement cost |  | $ 413 | $ 977 | $ 1,103
Assumptions |  |  |  |
Discount rate |  | 3.75% | 4.00% | 4.00%
Expected return on plan assets |  | 6.50% | 6.50% | 6.50%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) |  | $ (4,739) | $ 1,199 |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  | (2,887) | (2,849) |
Defined Benefit Plan, Plan Assets, Amount |  | 43,601 | 48,396 | $ 43,272
Defined Benefit Plan, Plan Assets, Contributions by Employer |  | 1,205 | 1,948 |
Defined Benefit Plan, Plan Assets, Benefits Paid |  | (2,887) | (2,849) |
Funded status |  | (15,776) | (16,268) |
Defined Benefit Plan Accrued Pension Costs Accrued Expenses Employment Benefits |  | $ 15,776 | $ 16,268 |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 4.25% | 3.75% |
[1] | As a result of our adoption of ASU 2017-07 on January 1, 2018, the "other than service" cost components of the net periodic costs have been recorded or reclassified to other income (expense), net in the condensed consolidated statements of income.
[2] | 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 gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. + 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)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + 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 (k)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + 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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