Debt Obligations - Schedule of Notes Payable (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Long Term Debt
Gross amount of debt	$ 1,742,269,000	$ 1,712,886,000
Less: unamortized debt issuance costs	(18,139,000)	(19,133,000)
Total debt obligations	1,724,130,000	1,693,753,000
Credit facility at a floating rate of interest of one-month LIBOR plus 1.75% at March 31, 2021, secured by engines. The facility has a committed amount of $1.0 billion at March 31, 2021, which revolves until the maturity date of June 2024
Long Term Debt
Line of credit facility outstanding amount	$ 817,000,000	777,000,000
WEST V Series A 2020 term notes payable at a fixed rate of interest of 3.23%, maturing in March 2045, secured by engines
Long Term Debt
Fixed rate (as a percent)	3.23%
Gross amount of debt	$ 283,533,000	286,863,000
WEST V Series B 2020 term notes payable at a fixed rate of interest of 4.21%, maturing in March 2045, secured by engines
Long Term Debt
Fixed rate (as a percent)	4.21%
Gross amount of debt	$ 39,395,000	39,855,000
WEST V Series C 2020 term notes payable at a fixed rate of interest of 6.66%, maturing in March 2045, secured by engines
Long Term Debt
Fixed rate (as a percent)	6.66%
Gross amount of debt	$ 18,617,000	19,043,000
WEST IV Series A 2018 term notes payable at a fixed rate of interest of 4.75%, maturing in September 2043, secured by engines
Long Term Debt
Fixed rate (as a percent)	4.75%
Gross amount of debt	$ 275,042,000	277,481,000
WEST IV Series B 2018 term notes payable at a fixed rate of interest of 5.44%, maturing in September 2043, secured by engines
Long Term Debt
Fixed rate (as a percent)	5.44%
Gross amount of debt	$ 39,476,000	39,640,000
WEST III Series A 2017 term notes payable at a fixed rate of interest of 4.69%, maturing in August 2042, secured by engines
Long Term Debt
Fixed rate (as a percent)	4.69%
Gross amount of debt	$ 224,401,000	227,138,000
WEST III Series B 2017 term notes payable at a fixed rate of interest of 6.36%, maturing in August 2042, secured by engines
Long Term Debt
Fixed rate (as a percent)	6.36%
Gross amount of debt	$ 32,195,000	32,481,000
Note payable at three-month LIBOR plus a margin ranging from 1.85% to 2.50% at March 31, 2021, maturing in July 2022, secured by engines
Long Term Debt
Gross amount of debt	$ 5,843,000	6,138,000
Note payable at a fixed rate of interest of 3.18%, maturing in July 2024, secured by an aircraft
Long Term Debt
Fixed rate (as a percent)	3.18%
Gross amount of debt	$ 6,767,000	$ 7,247,000
Revolving credit facility \| Credit facility at a floating rate of interest of one-month LIBOR plus 1.75% at March 31, 2021, secured by engines. The facility has a committed amount of $1.0 billion at March 31, 2021, which revolves until the maturity date of June 2024
Long Term Debt
Line of credit facility, maximum borrowing capacity	$ 1,000,000,000.0
LIBOR \| Credit facility at a floating rate of interest of one-month LIBOR plus 1.75% at March 31, 2021, secured by engines. The facility has a committed amount of $1.0 billion at March 31, 2021, which revolves until the maturity date of June 2024
Long Term Debt
Variable rate (as a percent)	1.75%
LIBOR \| Note payable at three-month LIBOR plus a margin ranging from 1.85% to 2.50% at March 31, 2021, maturing in July 2022, secured by engines \| Minimum
Long Term Debt
Variable rate (as a percent)	1.85%
LIBOR \| Note payable at three-month LIBOR plus a margin ranging from 1.85% to 2.50% at March 31, 2021, maturing in July 2022, secured by engines \| Maximum
Long Term Debt
Variable rate (as a percent)	2.50%

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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