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v3.20.4

Debt Obligations - Narrative (Details) | 1 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2020 USD ($) | Dec. 31, 2020 USD ($) engine | Dec. 31, 2019 USD ($) | Mar. 31, 2020 USD ($) | Mar. 31, 2020 | Mar. 31, 2020 engine | Mar. 31, 2020 airframe | Jul. 31, 2019 | Jun. 30, 2019 USD ($) | Feb. 28, 2019 USD ($) | Dec. 31, 2018 USD ($)
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Loss on extinguishment of debt |  | $ 4,688,000 | $ 220,000 |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 1,712,886,000 | 1,270,469,000 |  |  |  |  |  |  |  |
WEST V |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of assets used to secure debt |  |  |  |  |  | 54 | 3 |  |  |  |
WEST V | Assets Under Purchase Agreement With WEST V [Member] |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of assets used to secure debt |  |  |  |  |  | 25 | 3 |  |  |  |
WEST V Notes | WEST V |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  | $ 366,200,000 |  |  |  |  |  |  |
WEST V Series A Notes |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fixed rate |  | 3.23% |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 286,863,000 | 0 |  |  |  |  |  |  |  |
WEST V Series A Notes | WEST V |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  | 303,000,000.0 |  |  |  |  |  |  |
Fixed rate |  |  |  |  | 3.228% |  |  |  |  |  |
Debt term | 8 years |  |  |  |  |  |  |  |  |  |
Notes issue price, percentage of par | 99.99859% |  |  |  |  |  |  |  |  |  |
WEST V Series B Notes |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fixed rate |  | 4.21% |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 39,855,000 | 0 |  |  |  |  |  |  |  |
WEST V Series B Notes | WEST V |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  | 42,100,000 |  |  |  |  |  |  |
Fixed rate |  |  |  |  | 4.212% |  |  |  |  |  |
Debt term | 8 years |  |  |  |  |  |  |  |  |  |
Notes issue price, percentage of par | 99.99493% |  |  |  |  |  |  |  |  |  |
WEST V Series C Notes |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fixed rate |  | 6.66% |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 19,043,000 | 0 |  |  |  |  |  |  |  |
WEST V Series C Notes | WEST V |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  |  | $ 21,100,000 |  |  |  |  |  |  |
Fixed rate |  |  |  |  | 6.657% |  |  |  |  |  |
Debt term | 8 years |  |  |  |  |  |  |  |  |  |
Notes issue price, percentage of par | 99.99918% |  |  |  |  |  |  |  |  |  |
WEST II Notes |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Loss on extinguishment of debt | $ 4,700,000 |  |  |  |  |  |  |  |  |  |
Note payable at a fixed rate of interest of 3.18%, maturing in July 2024, secured by an aircraft |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fixed rate |  | 3.18% |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 7,247,000 | 9,124,000 |  |  |  |  |  |  |  |
Note payable due July 2022 |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of assets used to secure debt | engine |  | 2 |  |  |  |  |  |  |  |  |
Long-term debt outstanding |  | $ 6,138,000 | 7,286,000 |  |  |  |  |  |  | $ 8,100,000 |
Maximum | Note payable at a fixed rate of interest of 3.18%, maturing in July 2024, secured by an aircraft |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fixed rate |  |  |  |  |  |  |  | 3.18% |  |  |
LIBOR | Revolving credit facility |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Variable rate spread |  | 1.38% |  |  |  |  |  |  |  |  |
LIBOR | Minimum | Note payable due July 2022 |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Variable rate spread |  | 1.85% |  |  |  |  |  |  |  |  |
LIBOR | Maximum | Note payable due July 2022 |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Variable rate spread |  | 2.50% |  |  |  |  |  |  |  |  |
Revolving credit facility | Revolving credit facility |  |  |  |  |  |  |  |  |  |  |
Long Term Debt [Line Items] |  |  |  |  |  |  |  |  |  |  |
Line of credit facility maximum borrowing Capacity before amendment |  |  |  |  |  |  |  |  |  |  | $ 890,000,000.0
Line of credit facility, maximum borrowing capacity |  |  |  |  |  |  |  |  | $ 1,000,000,000.0 |  |
Line of credit facility, maximum borrowing capacity under accordion feature |  | $ 1,300,000,000 |  |  |  |  |  |  |  |  |
Debt issuance costs, line of credit |  |  |  |  |  |  |  |  | $ 2,800,000 |  |
Loss on extinguishment of debt |  | 200,000 |  |  |  |  |  |  |  |  |
Line of credit facility, remaining borrowing capacity |  | $ 223,000,000.0 | $ 603,000,000.0 |  |  |  |  |  |  |  |

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