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Notes Payable (Details) |  |  |  |  |  |  |  |  |  | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jul. 10, 2015 USD ($) | Mar. 25, 2015 USD ($) | Dec. 31, 2014 USD ($) item | Jul. 16, 2014 USD ($) | Jun. 04, 2014 USD ($) | Jan. 10, 2014 engine | Sep. 18, 2013 USD ($) | Sep. 28, 2012 USD ($) | Sep. 17, 2012 USD ($) engine | Dec. 31, 2015 USD ($) engine item | Dec. 31, 2014 USD ($) item | Dec. 31, 2013 USD ($) | Jun. 30, 2015 USD ($) item
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | $ 840,956,000 |  |  |  |  |  |  | $ 878,684,000 | $ 840,956,000 |  |
One-month LIBOR rate (as a percent) |  |  | 0.17% |  |  |  |  |  |  | 0.43% | 0.17% |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
2016 |  |  |  |  |  |  |  |  |  | $ 22,702,000 |  |  |
2017 |  |  |  |  |  |  |  |  |  | 23,718,000 |  |  |
2018 |  |  |  |  |  |  |  |  |  | 33,391,000 |  |  |
2019 (includes $549.0 million outstanding on revolving credit facility) |  |  |  |  |  |  |  |  |  | 572,529,000 |  |  |
2020 |  |  |  |  |  |  |  |  |  | 23,127,000 |  |  |
Thereafter |  |  |  |  |  |  |  |  |  | 203,217,000 |  |  |
Notes payable |  |  | $ 840,956,000 |  |  |  |  |  |  | 878,684,000 | $ 840,956,000 |  |
Line of credit facility outstanding amount |  |  |  |  |  |  |  |  |  | 549,000,000 |  |  |
Notes payable |  |  | $ 840,956,000 |  |  |  |  |  |  | 878,684,000 | 840,956,000 |  |
Net proceeds received from notes issued and sold |  |  |  |  |  |  |  |  |  | $ 192,700,000 | $ 154,395,000 | $ 130,000,000 |
WOLF |  |  |  |  |  |  |  |  |  |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition of remaining outstanding shares of previously held equity method investment (as a percent) |  |  |  |  |  |  | 50.00% |  |  |  |  |  |
Controlling interest assumed (as a percent) |  |  |  |  |  |  | 100.00% |  |  |  |  |  |
WEST II Series 2012-A term notes payable at a fixed rate of interest maturing in September 2037. Secured by engines | WEST II |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed rate (as a percent) |  |  | 5.50% |  |  |  |  |  |  | 5.50% | 5.50% |  |
Notes payable |  |  | $ 351,899,000 |  |  |  |  |  |  | $ 300,467,000 | $ 351,899,000 |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | 351,899,000 |  |  |  |  |  |  | $ 300,467,000 | 351,899,000 |  |
Maturity term |  |  |  |  |  |  |  |  |  | 10 years |  |  |
Face amount |  |  |  |  |  |  |  |  | $ 390,000,000 |  |  |  |
Net proceeds received from notes issued and sold |  |  |  |  |  |  |  |  | 384,900,000 |  |  |  |
Number of engines in portfolio offered as collateral | item |  |  |  |  |  |  |  |  |  | 63 |  |  |
Number of business days to pay interest |  |  |  |  |  |  |  |  |  | 5 days |  |  |
WEST II Series 2012-A term notes payable at a fixed rate of interest maturing in September 2037. Secured by engines | WEST II | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum amount of cash from maintenance reserve payments required to be held in restricted cash account |  |  |  |  |  |  |  |  |  | $ 9,000,000 |  |  |
Note payable at fixed interest rates ranging from 2.60% to 2.97%, maturing in July 2024. Secured by an aircraft |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Initial term for interest payment |  |  |  |  |  |  |  |  |  | 5 years |  |  |
Notes payable |  |  | 12,909,000 |  |  |  |  |  |  | $ 16,135,000 | 12,909,000 |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | 12,909,000 |  |  |  |  |  |  | $ 16,135,000 | 12,909,000 |  |
Maturity term |  |  |  | 10 years |  |  |  |  |  |  |  |  |
Face amount |  |  |  | $ 13,400,000 |  |  |  |  |  |  |  |  | $ 4,700,000
Number of term notes held | item |  |  |  |  |  |  |  |  |  |  |  |  | 2
Note payable at fixed interest rates ranging from 2.60% to 2.97%, maturing in July 2024. Secured by an aircraft | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed rate (as a percent) |  |  |  |  |  |  |  |  |  | 2.60% |  |  |
Note payable at fixed interest rates ranging from 2.60% to 2.97%, maturing in July 2024. Secured by an aircraft | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed rate (as a percent) |  |  |  |  |  |  |  |  |  | 2.97% |  |  |
Note payable at a fixed interest rate of 2.25%, maturing in January 2018, secured by engines |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | 14,455,000 |  |  |  |  |  |  | $ 13,082,000 | 14,455,000 |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | 14,455,000 |  |  |  |  |  |  | $ 13,082,000 | $ 14,455,000 |  |
Maturity term |  |  |  |  |  | 4 years |  |  |  |  |  |  |
Number of engines pledged as collateral | engine |  |  |  |  |  | 3 |  |  |  |  |  |  |
Note payable at a fixed interest rate of 2.25%, maturing in January 2018, secured by engines | LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate (as a percent) |  |  |  |  |  |  |  |  |  | 2.25% |  |  |
Note payable at a fixed interest rate of 2.25%, maturing in January 2018, secured by engines | One-month LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed rate (as a percent) |  |  |  |  |  | 2.25% |  |  |  |  |  |  |
Note payable at a fixed interest rate of 4.00%, maturing in March 2015, secured by engines |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate (as a percent) |  |  |  |  |  |  |  |  |  |  | 4.00% |  |
Notes payable |  |  | 24,000,000 |  |  |  |  |  |  |  | $ 24,000,000 |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | 24,000,000 |  |  |  |  |  |  |  | 24,000,000 |  |
Note payable at a fixed interest rate of 5.50%, maturing in July 2015. Secured by one engin. |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Fixed rate (as a percent) |  |  |  |  |  |  |  |  |  | 5.50% |  |  |
Notes payable |  |  | 7,693,000 |  |  |  |  |  |  |  | 7,693,000 |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | $ 7,693,000 |  |  |  |  |  |  |  | $ 7,693,000 |  |
Maturity term |  |  |  |  |  |  |  | 5 years |  |  |  |  |
Face amount |  |  |  |  |  |  |  | $ 8,700,000 |  |  |  |  |
Loan Paid off | $ 7,400,000 |  |  |  |  |  |  |  |  |  |  |  |
Number of engines pledged as collateral | engine |  |  |  |  |  |  |  |  |  | 1 |  |  |
Prior WEST notes |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  |  |  |  |  |  |  | 435,900,000 |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  |  |  |  |  |  |  | $ 435,900,000 |  |  |  |
Notes payable Member |  |  |  |  |  |  |  |  |  |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  |  |  |  |  |  |  |  | $ 878,700,000 |  |  |
Interest rate, minimum (as a percent) |  |  |  |  |  |  |  |  |  | 2.60% |  |  |
Interest rate, maximum (as a percent) |  |  |  |  |  |  |  |  |  | 5.50% |  |  |
Notes payable Member | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity term |  |  |  |  |  |  |  |  |  | 2 years |  |  |
Notes payable Member | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity term |  |  |  |  |  |  |  |  |  | 8 years 7 months 6 days |  |  |
Revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity under credit facility |  |  |  |  | $ 700,000,000 |  |  |  |  |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Leverage ratio |  |  | 4.46 |  |  |  |  |  |  |  | 4.46 |  |
Remaining borrowing capacity available |  |  | $ 270,000,000 |  |  |  |  |  |  | $ 151,000,000 | $ 270,000,000 |  |
Debt issuance costs |  |  |  |  | 4,900,000 |  |  |  |  |  |  |  |
Maximum borrowing capacity under credit facility before amendment |  |  |  |  | $ 450,000,000 |  |  |  |  |  |  |  |
Extended maturity term |  |  |  |  | 5 years |  |  |  |  |  |  |  |
Revolving credit facility | One-month LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Variable rate of debt |  |  | one-month LIBOR |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate (as a percent) |  |  | 2.75% |  |  |  |  |  |  |  |  |  |
Revolving credit facility | WEST |  |  |  |  |  |  |  |  |  |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Number of engines pledged as collateral | engine |  |  |  |  |  |  |  |  | 22 |  |  |  |
Revolving credit facility | Credit agreement | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Interest coverage ratio |  |  |  |  |  |  |  |  |  | 2.25 |  |  |
Revolving credit facility | Credit agreement | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Leverage ratio |  |  |  |  |  |  |  |  |  | 5.00 |  |  |
Credit facility at a floating rate of interest of LIBOR plus 2.75%, secured by engines |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum borrowing capacity under credit facility |  |  |  |  |  |  |  |  |  | $ 700,000,000 |  |  |
Notes payable |  |  | $ 430,000,000 |  |  |  |  |  |  | 549,000,000 | 430,000,000 |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | 430,000,000 |  |  |  |  |  |  | $ 549,000,000 | $ 430,000,000 |  |
Credit facility at a floating rate of interest of LIBOR plus 2.75%, secured by engines | LIBOR |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate (as a percent) |  |  |  |  |  |  |  |  |  | 2.75% | 2.75% |  |
Term notes | WOLF |  |  |  |  |  |  |  |  |  |  |  |  |
Long Term Debt |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | 24,000,000 |  |  |  |  |  |  |  | $ 24,000,000 |  |
Principal outstanding repayable |  |  |  |  |  |  |  |  |  |  |  |  |
Notes payable |  |  | $ 24,000,000 |  |  |  |  |  |  |  | $ 24,000,000 |  |
Face amount |  |  |  |  |  |  | $ 36,000,000 |  |  |  |  |  |
Loan Paid off |  | $ 23,100,000 |  |  |  |  |  |  |  |  |  |  |
Discount (in percentage) |  | 5.00% |  |  |  |  |  |  |  |  |  |  |
Number of term notes held | item |  |  | 2 |  |  |  |  |  |  |  | 2 |  |

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- Definition Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 + Details
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