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Note 11 - Pension Plan and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Pension Plan [Member] |  |  |  |
Service Cost |  | $ 5,491 | $ 6,459 | $ 5,629
Interest Cost |  | 14,412 | 13,452 | 14,139
Expected Return on Assets |  | (21,297) | (21,199) | (19,229)
From Regulatory Asset |  | 5 | 16 | 120
From Other Comprehensive Income | [1] | 9 | 0 | 3
From Regulatory Asset |  | 4,642 | 7,135 | 5,090
From Other Comprehensive Income | [1] | 114 | 183 | 125
Net Periodic Pension Cost | [2] | 3,376 | 6,046 | 5,877
From Other Comprehensive Income | [1] | 114 | 183 | 125
Amortization of Prior Service Cost |  |  |  |
From Regulatory Asset |  | 5 | 16 | 120
From Other Comprehensive Income | [1] | 9 | 0 | 3
Amortization of Net Actuarial Loss |  |  |  |
From Regulatory Asset |  | (4,642) | (7,135) | (5,090)
From Other Comprehensive Income | [1] | 114 | 183 | 125
Net Periodic Pension Cost | [2] | 3,376 | 6,046 | 5,877
Pension Plan [Member] | Costs Included in OTP Capital Expenditures [Member] |  |  |  |
Net Periodic Pension Cost |  | 1,365 | 1,542 | 1,094
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 1,365 | 1,542 | 1,094
Pension Plan [Member] | Costs Included in Electric Operation and Maintenance Expenses [Member] |  |  |  |
Net Periodic Pension Cost |  | 3,994 | 4,756 | 4,400
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 3,994 | 4,756 | 4,400
Pension Plan [Member] | Costs Included in Other Nonelectric Expenses [Member] |  |  |  |
Net Periodic Pension Cost |  | 132 | 161 | 135
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 132 | 161 | 135
Pension Plan [Member] | Nonservice Costs Included in Nonservice Cost Components of Postretirement Benefits [Member] |  |  |  |
Net Periodic Pension Cost |  | (1,589) | (314) | 200
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | (1,589) | (314) | 200
Pension Plan [Member] | Nonservice Costs Capitalized as Regulatory Assets [Member] |  |  |  |
Net Periodic Pension Cost |  | (526) | (99) | 48
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | (526) | (99) | 48
Executive Survivor and Supplemental Retirement Plan [Member] |  |  |  |
Service Cost |  | 418 | 408 | 290
Interest Cost |  | 1,735 | 1,589 | 1,686
From Regulatory Asset |  | 5 | 20 | 16
From Other Comprehensive Income | [3] | 17 | 34 | 38
From Regulatory Asset |  | 124 | 206 | 285
From Other Comprehensive Income | [3] | 348 | 722 | 440
Net Periodic Pension Cost | [4] | 2,647 | 2,979 | 2,755
From Other Comprehensive Income | [3] | 348 | 722 | 440
Amortization of Prior Service Cost |  |  |  |
From Regulatory Asset |  | 5 | 20 | 16
From Other Comprehensive Income | [3] | 17 | 34 | 38
Amortization of Net Actuarial Loss |  |  |  |
From Regulatory Asset |  | (124) | (206) | (285)
From Other Comprehensive Income | [3] | 348 | 722 | 440
Net Periodic Pension Cost | [4] | 2,647 | 2,979 | 2,755
Executive Survivor and Supplemental Retirement Plan [Member] | Costs Included in Electric Operation and Maintenance Expenses [Member] |  |  |  |
Net Periodic Pension Cost |  | 104 | 99 | 94
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 104 | 99 | 94
Executive Survivor and Supplemental Retirement Plan [Member] | Costs Included in Other Nonelectric Expenses [Member] |  |  |  |
Net Periodic Pension Cost |  | 314 | 309 | 196
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 314 | 309 | 196
Executive Survivor and Supplemental Retirement Plan [Member] | Nonservice Costs Included in Nonservice Cost Components of Postretirement Benefits [Member] |  |  |  |
Net Periodic Pension Cost |  | 2,229 | 2,571 | 2,465
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 2,229 | 2,571 | 2,465
Other Postretirement Benefits Plan [Member] |  |  |  |
Service Cost |  | 1,286 | 1,526 | 1,425
Interest Cost |  | 3,083 | 2,583 | 2,712
From Regulatory Asset |  | 0 | 0 | (4)
From Other Comprehensive Income | [1] | 0 | 0 | 4
From Regulatory Asset |  | (1,571) | (1,648) | (936)
From Other Comprehensive Income | [1] | 38 | 42 | 19
Net Periodic Pension Cost | [5] | 5,978 | 5,799 | 5,092
From Other Comprehensive Income | [1] | 38 | 42 | 19
Amortization of Prior Service Cost |  |  |  |
From Regulatory Asset |  | 0 | 0 | (4)
From Other Comprehensive Income | [1] | 0 | 0 | 4
Amortization of Net Actuarial Loss |  |  |  |
From Regulatory Asset |  | 1,571 | 1,648 | 936
From Other Comprehensive Income | [1] | 38 | 42 | 19
Net Periodic Pension Cost | [5] | 5,978 | 5,799 | 5,092
Effect of Medicare Part D Subsidy |  | (179) | (470) | (561)
Other Postretirement Benefits Plan [Member] | Costs Included in OTP Capital Expenditures [Member] |  |  |  |
Net Periodic Pension Cost |  | 320 | 364 | 277
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 320 | 364 | 277
Other Postretirement Benefits Plan [Member] | Costs Included in Electric Operation and Maintenance Expenses [Member] |  |  |  |
Net Periodic Pension Cost |  | 935 | 1,124 | 1,114
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 935 | 1,124 | 1,114
Other Postretirement Benefits Plan [Member] | Costs Included in Other Nonelectric Expenses [Member] |  |  |  |
Net Periodic Pension Cost |  | 31 | 38 | 34
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 31 | 38 | 34
Other Postretirement Benefits Plan [Member] | Nonservice Costs Included in Nonservice Cost Components of Postretirement Benefits [Member] |  |  |  |
Net Periodic Pension Cost |  | 3,525 | 3,253 | 2,955
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | 3,525 | 3,253 | 2,955
Other Postretirement Benefits Plan [Member] | Nonservice Costs Capitalized as Regulatory Assets [Member] |  |  |  |
Net Periodic Pension Cost |  | 1,167 | 1,020 | 712
Amortization of Net Actuarial Loss |  |  |  |
Net Periodic Pension Cost |  | $ 1,167 | $ 1,020 | $ 712
[1] | Corporate cost included in nonservice cost components of postretirement benefits.
[2] | Allocation of Costs: 2019 2018 2017 Service costs included in OTP Capital Expenditures $ 1,365 $ 1,542 $ 1,094 Service costs included in electric operation and maintenance expenses 3,994 4,756 4,400 Service costs included in other nonelectric expenses 132 161 135 Nonservice costs capitalized (526 ) (99 ) 48 Nonservice costs included in nonservice cost components of postretirement benefits (1,589 ) (314 ) 200
[3] | Amortization of prior service costs and net actuarial losses from other comprehensive income are included in nonservice cost components of postretirement benefits.
[4] | Allocation of Costs: 2019 2018 2017 Service costs included in electric operation and maintenance expenses $ 104 $ 99 $ 94 Service costs included in other nonelectric expenses 314 309 196 Nonservice costs included in nonservice cost components of postretirement benefits 2,229 2,571 2,465
[5] | Allocation of Cost: 2019 2018 2017 Service Costs included in OTP capital expenditures $ 320 $ 364 $ 277 Service costs included in electric operation and maintenance expenses 935 1,124 1,114 Service costs included in other nonelectric expenses 31 38 34 Nonservice costs capitalized 1,167 1,020 712 Nonservice costs included in nonservice cost components of postretirement benefits 3,525 3,253 2,955

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