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Retirement Plans and Employee Stock Purchase Plans - Retirement Plans (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
SkyWest Plan |  |  |
Retirement Plans |  |  |
Service period required to be completed to be eligible to participate in plan | 90 days |  |
Required age for an employee to be eligible to participate in plan | 18 years |  |
Percentage of employer matching contribution based on length of service | 100.00% |  |
Minimum benefit plan percentage of participants compensation eligible for employer matching contribution based on position and years of service | 2.00% |  |
Maximum benefit plan percentage of participants compensation eligible for employer matching contribution based on position and years of service | 7.00% |  |
Company's combined contributions | $ 26.1 | $ 23.2 | $ 20.4
Atlantic Southeast and the ExpressJet Plans |  |  |
Retirement Plans |  |  |
Service period required to be completed to be eligible to participate in plan | 90 days |  |
Required age for an employee to be eligible to participate in plan | 18 years |  |
Company's combined contributions | $ 17.8 | $ 21.0 | $ 24.0
Maximum percentage of participant's total compensation eligible for employer matching contribution | 8.00% |  |
Atlantic Southeast Plan |  |  |
Retirement Plans |  |  |
Percentage of vesting for plan participants' elective deferrals and rollover amounts | 100.00% |  |
Atlantic Southeast Plan | Minimum |  |  |
Retirement Plans |  |  |
Percentage of vesting of company matching contribution based on length of service | 10.00% |  |
Atlantic Southeast Plan | Maximum |  |  |
Retirement Plans |  |  |
Percentage of vesting of company matching contribution based on length of service | 100.00% |  |

X
- Definition Represents the maximum percentage of the participant's compensation eligible for the employer matching contribution. + References No definition available. + Details
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- Definition Represents the maximum percentage of the employer's matching contribution for participant contributions based upon the length of service. + References No definition available. + Details
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- Definition Represents the age required to be completed by the employee to be eligible to participate in the plan. + References No definition available. + Details
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- Definition Description of the estimated period of time over which an employee is required to provide service to participate in the defined benefit plan. + References No definition available. + Details
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- Definition Represents the percentage of vesting for plan participants in their elective deferrals and rollover amounts. + References No definition available. + Details
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- Definition Represents the percentage of vesting of company matching contribution for plan participants based on the length of service. + References No definition available. + Details
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- Definition Represents the maximum benefit plan percentage of participants compensation eligible for employer matching contribution based on position and years of service. + References No definition available. + Details
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- Definition Represents the minimum benefit plan percentage of participants compensation eligible for employer matching contribution based on position and years of service. + References No definition available. + Details
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