The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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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 depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Stated as a percentage, the estimated or actual value of the asset at the end of its useful life or when it is no longer serviceable (cannot be used for its original purpose) divided by its [historical] capitalized cost.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Summary of Significant Accounting Policies - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Depreciation	$ 38,000	$ 32,000	$ 45,000
Intangible amortization	0	1,000	1,000
Total depreciation and amortization	38,000	33,000	$ 46,000
Property and equipment, net	$ 186,000	176,000
Aircraft
Property, Plant and Equipment [Line Items]
Useful life	25 years
Residual Value	10.00%
Aircraft rotable parts
Property, Plant and Equipment [Line Items]
Residual Value	10.00%
Ground property and equipment \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Ground property and equipment \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Ground equipment leasehold improvements \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Capitalized software
Property, Plant and Equipment [Line Items]
Property and equipment, net	$ 9,000	$ 8,000
Capitalized software \| Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Capitalized software \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Buildings
Property, Plant and Equipment [Line Items]
Residual Value	10.00%
Buildings \| Maximum
Property, Plant and Equipment [Line Items]
Useful life	40 years