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Note 10 - Short-term and Long-term Borrowings - Breakdown of Assignment of Consolidated Short-term and Long-term Debt Outstanding (Details) - USD ($) $ in Thousands | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Short-Term Debt |  | $ 41,239 | $ 6,000
Long-Term Debt |  | 727,261 | 692,351
Less: Current Maturities net of Unamortized Debt Issuance Costs |  | 261 | 183
Unamortized Long-Term Debt Issuance Costs |  | 2,611 | 2,587
Total Long-Term Debt net of Unamortized Debt Issuance Costs |  | 724,389 | 689,581
Total Short-Term and Long-Term Debt (with current maturities) |  | 765,889 | 695,764
Short-Term Debt |  | 41,239 | 6,000
The 3.55% Guaranteed Senior Notes, Due December 15, 2026 [Member] |  |  |
Long-Term Debt |  | $ 80,000 | $ 80,000
Debt Instrument, Interest Rate, Stated Percentage |  | 3.55% | 3.55%
Senior Unsecured Notes 4.63%, Series 2011A, due December 1, 2021 [Member] |  |  |
Long-Term Debt |  | $ 140,000 | $ 140,000
Debt Instrument, Interest Rate, Stated Percentage |  | 4.63% | 4.63%
Senior Unsecured Notes 6.15%, Series 2007B, due August 20, 2022 [Member] |  |  |
Long-Term Debt |  | $ 30,000 | $ 30,000
Debt Instrument, Interest Rate, Stated Percentage |  | 6.15% | 6.15%
Senior Unsecured Notes 6.37%, Series C, Due August 20, 2027 [Member] |  |  |
Long-Term Debt |  | $ 42,000 | $ 42,000
Debt Instrument, Interest Rate, Stated Percentage |  | 6.37% | 6.37%
Senior Unsecured Notes 4.68%, Series 2013A, due February 27, 2029 [Member] |  |  |
Long-Term Debt |  | $ 60,000 | $ 60,000
Debt Instrument, Interest Rate, Stated Percentage |  | 4.68% | 4.68%
Senior Unsecured Notes 3.07%, Series 2019A, due October 10, 2029 [Member] |  |  |
Long-Term Debt | [1] | $ 10,000 | $ 10,000
Debt Instrument, Interest Rate, Stated Percentage |  | 3.07% | 3.07%
Senior Unsecured Notes 3.22%, Series 2020A, due February 25, 2030 [Member] |  |  |
Long-Term Debt |  | $ 10,000 |
Debt Instrument, Interest Rate, Stated Percentage |  | 3.22% |
Senior Unsecured Notes 6.47%, Series 2007D, due August 20, 2037 [Member] |  |  |
Long-Term Debt |  | $ 50,000 | $ 50,000
Debt Instrument, Interest Rate, Stated Percentage |  | 6.47% | 6.47%
Senior Unsecured Notes 3.52%, Series 2019B, Due October 10, 2039 [Member] |  |  |
Long-Term Debt |  | $ 26,000 | $ 26,000
Debt Instrument, Interest Rate, Stated Percentage |  | 3.52% | 3.52%
Senior Unsecured Notes 3.62%. Series 2020C, due February 25, 2040 [Member] |  |  |
Long-Term Debt |  | $ 10,000 |
Debt Instrument, Interest Rate, Stated Percentage |  | 3.62% |
Senior Unsecured Notes 5.47%, Series 2013B, due February 27, 2044 [Member] |  |  |
Long-Term Debt |  | $ 90,000 | $ 90,000
Debt Instrument, Interest Rate, Stated Percentage |  | 5.47% | 5.47%
Senior Unsecured Notes 4.07%, Series 2018A, Due February 7, 2048 [Member] |  |  |
Long-Term Debt |  | $ 100,000 | $ 100,000
Debt Instrument, Interest Rate, Stated Percentage |  | 4.07% | 4.07%
Senior Unsecured Notes 3.82%, Series 2019C, due October 10, 2049 [Member] |  |  |
Long-Term Debt |  | $ 64,000 | $ 64,000
Debt Instrument, Interest Rate, Stated Percentage |  | 3.82% | 3.82%
Senior Unsecured Notes 3.92%, Series 2020D, due February 25, 2050 [Member] |  |  |
Long-Term Debt |  | $ 15,000 |
Debt Instrument, Interest Rate, Stated Percentage |  | 3.92% |
PACE Note, 2.54%, due March 18, 2021 [Member] |  |  |
Long-Term Debt |  | $ 261 | $ 351
Debt Instrument, Interest Rate, Stated Percentage |  | 2.54% | 2.54%
Parent Company [Member] |  |  |
Short-Term Debt |  | $ 41,239 | $ 6,000
Long-Term Debt |  | 80,261 | 80,351
Less: Current Maturities net of Unamortized Debt Issuance Costs |  | 261 | 183
Unamortized Long-Term Debt Issuance Costs |  | 330 | 356
Total Long-Term Debt net of Unamortized Debt Issuance Costs |  | 79,670 | 79,812
Total Short-Term and Long-Term Debt (with current maturities) |  | 121,170 | 85,995
Short-Term Debt |  | 41,239 | 6,000
Parent Company [Member] | The 3.55% Guaranteed Senior Notes, Due December 15, 2026 [Member] |  |  |
Long-Term Debt |  | $ 80,000 | $ 80,000
Debt Instrument, Interest Rate, Stated Percentage |  | 3.55% | 3.55%
Parent Company [Member] | PACE Note, 2.54%, due March 18, 2021 [Member] |  |  |
Long-Term Debt |  | $ 261 | $ 351
Debt Instrument, Interest Rate, Stated Percentage |  | 2.54% | 2.54%
Otter Tail Power Company [Member] |  |  |
Long-Term Debt |  | $ 647,000 | $ 612,000
Unamortized Long-Term Debt Issuance Costs |  | 2,281 | 2,231
Total Long-Term Debt net of Unamortized Debt Issuance Costs |  | 644,719 | 609,769
Total Short-Term and Long-Term Debt (with current maturities) |  | 644,719 | 609,769
Otter Tail Power Company [Member] | Senior Unsecured Notes 4.63%, Series 2011A, due December 1, 2021 [Member] |  |  |
Long-Term Debt |  | $ 140,000 | $ 140,000
Debt Instrument, Interest Rate, Stated Percentage |  | 4.63% | 4.63%
Otter Tail Power Company [Member] | Senior Unsecured Notes 6.15%, Series 2007B, due August 20, 2022 [Member] |  |  |
Long-Term Debt |  | $ 30,000 | $ 30,000
Debt Instrument, Interest Rate, Stated Percentage |  | 6.15% | 6.15%
Otter Tail Power Company [Member] | Senior Unsecured Notes 6.37%, Series C, Due August 20, 2027 [Member] |  |  |
Long-Term Debt |  | $ 42,000 | $ 42,000
Debt Instrument, Interest Rate, Stated Percentage |  | 6.37% | 6.37%
Otter Tail Power Company [Member] | Senior Unsecured Notes 4.68%, Series 2013A, due February 27, 2029 [Member] |  |  |
Long-Term Debt |  | $ 60,000 | $ 60,000
Debt Instrument, Interest Rate, Stated Percentage |  | 4.68% | 4.68%
Otter Tail Power Company [Member] | Senior Unsecured Notes 3.07%, Series 2019A, due October 10, 2029 [Member] |  |  |
Long-Term Debt | [1] | $ 10,000 | $ 10,000
Debt Instrument, Interest Rate, Stated Percentage |  | 3.07% | 3.07%
Otter Tail Power Company [Member] | Senior Unsecured Notes 3.22%, Series 2020A, due February 25, 2030 [Member] |  |  |
Long-Term Debt |  | $ 10,000 |
Debt Instrument, Interest Rate, Stated Percentage |  | 3.22% |
Otter Tail Power Company [Member] | Senior Unsecured Notes 6.47%, Series 2007D, due August 20, 2037 [Member] |  |  |
Long-Term Debt |  | $ 50,000 | $ 50,000
Debt Instrument, Interest Rate, Stated Percentage |  | 6.47% | 6.47%
Otter Tail Power Company [Member] | Senior Unsecured Notes 3.52%, Series 2019B, Due October 10, 2039 [Member] |  |  |
Long-Term Debt |  | $ 26,000 | $ 26,000
Debt Instrument, Interest Rate, Stated Percentage |  | 3.52% | 3.52%
Otter Tail Power Company [Member] | Senior Unsecured Notes 3.62%. Series 2020C, due February 25, 2040 [Member] |  |  |
Long-Term Debt |  | $ 10,000 |
Debt Instrument, Interest Rate, Stated Percentage |  | 3.62% |
Otter Tail Power Company [Member] | Senior Unsecured Notes 5.47%, Series 2013B, due February 27, 2044 [Member] |  |  |
Long-Term Debt |  | $ 90,000 | $ 90,000
Debt Instrument, Interest Rate, Stated Percentage |  | 5.47% | 5.47%
Otter Tail Power Company [Member] | Senior Unsecured Notes 4.07%, Series 2018A, Due February 7, 2048 [Member] |  |  |
Long-Term Debt |  | $ 100,000 | $ 100,000
Debt Instrument, Interest Rate, Stated Percentage |  | 4.07% | 4.07%
Otter Tail Power Company [Member] | Senior Unsecured Notes 3.82%, Series 2019C, due October 10, 2049 [Member] |  |  |
Long-Term Debt |  | $ 64,000 | $ 64,000
Debt Instrument, Interest Rate, Stated Percentage |  | 3.82% | 3.82%
Otter Tail Power Company [Member] | Senior Unsecured Notes 3.92%, Series 2020D, due February 25, 2050 [Member] |  |  |
Long-Term Debt |  | $ 15,000 |
Debt Instrument, Interest Rate, Stated Percentage |  | 3.92% |
[1] | Holder is COBANK, a cooperative lender. Interest payments are subject to cash credits which may result in a lower effective interest rate.

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