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Debt Obligations - Narrative (Details) | 1 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Mar. 31, 2020 USD ($) | Sep. 30, 2020 USD ($) | Sep. 30, 2019 USD ($) | Sep. 30, 2020 USD ($) | Sep. 30, 2019 USD ($) | Mar. 31, 2020 USD ($) | Mar. 31, 2020 | Mar. 31, 2020 engine | Mar. 31, 2020 airframe
Long Term Debt |  |  |  |  |  |  |  |  |
Loss on debt extinguishment |  | $ 0 | $ 0 | $ 4,688,000 | $ 220,000 |  |  |  |
WEST V Series A Notes |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Fixed rate (as a percent) |  | 3.23% |  | 3.23% |  |  |  |  |
WEST V Series B Notes |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Fixed rate (as a percent) |  | 4.21% |  | 4.21% |  |  |  |  |
WEST V Series C Notes |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Fixed rate (as a percent) |  | 6.66% |  | 6.66% |  |  |  |  |
WEST II Series A Notes |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Fixed rate (as a percent) |  | 5.50% |  | 5.50% |  |  |  |  |
Loss on debt extinguishment | $ 4,700,000 |  |  |  |  |  |  |  |
WEST V |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Number of assets used to secure debt |  |  |  |  |  |  |  | 54 | 3
WEST V | WEST V Notes |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  |  | $ 366,200,000 |  |  |
WEST V | WEST V Series A Notes |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  |  | 303,000,000.0 |  |  |
Fixed rate (as a percent) |  |  |  |  |  |  | 3.228% |  |
Debt instrument, term | 8 years |  |  |  |  |  |  |  |
Notes issue price, percentage of par | 99.99859% |  |  |  |  |  |  |  |
WEST V | WEST V Series B Notes |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  |  | 42,100,000 |  |  |
Fixed rate (as a percent) |  |  |  |  |  |  | 4.212% |  |
Debt instrument, term | 8 years |  |  |  |  |  |  |  |
Notes issue price, percentage of par | 99.99493% |  |  |  |  |  |  |  |
WEST V | WEST V Series C Notes |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  |  |  | $ 21,100,000 |  |  |
Fixed rate (as a percent) |  |  |  |  |  |  | 6.657% |  |
Debt instrument, term | 8 years |  |  |  |  |  |  |  |
Notes issue price, percentage of par | 99.99918% |  |  |  |  |  |  |  |
Assets Under Purchase Agreement With WEST V | WEST V |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |
Number of assets used to secure debt |  |  |  |  |  |  |  | 25 | 3

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