Allegiant Travel (ALGT) 10-K 1 Mar 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 02, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Allegiant Travel CO
Document Type	10-K
Current Fiscal Year End Date	--12-31
Entity Public Float	$ 1,699,000,000
Entity Common Stock, Shares Outstanding		16,066,667
Amendment Flag	false
Entity Central Index Key	1,362,468
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Well Known Seasoned Issuer	Yes
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
CURRENT ASSETS:
Cash and cash equivalents	$ 59,449	$ 64,711
Restricted cash	11,190	11,647
Short-term investments	352,681	269,269
Accounts receivable	71,057	40,667
Expendable parts, supplies and fuel, net of reserve of $13,756 and $7,205	17,647	16,797
Prepaid expenses	23,931	16,277
Other current assets	5,320	2,686
TOTAL CURRENT ASSETS	541,275	422,054
Property and equipment, net of accumulated depreciation of $276,548 and $466,151 (including $112,750 and $0 from VIEs, Note 5)	1,512,415	1,095,314
Long-term investments	78,570	124,834
Deferred major maintenance, net of accumulated amortization of $8,218 and $1,510	31,326	17,347
Deposits and other assets	16,571	12,027
TOTAL ASSETS	2,180,157	1,671,576
CURRENT LIABILITIES:
Accounts payable	20,108	16,010
Accrued liabilities	105,127	96,661
Air traffic liability	210,184	194,001
Current maturities of notes payable, net of related costs of $2,298 and $1,868 (including $8,935 and $0 from VIEs, Note 5)	214,761	86,226
TOTAL CURRENT LIABILITIES	550,180	392,898
LONG-TERM DEBT AND OTHER LONG-TERM LIABILITIES:
Long-term debt, net of current maturities and related costs of $3,812 and $3,035 (including $92,424 and $0 from VIEs, Note 5)	950,131	722,048
Deferred income taxes	118,492	75,338
Other noncurrent liabilities	13,407	7,670
TOTAL LIABILITIES:	1,632,210	1,197,954
SHAREHOLDERS' EQUITY:
Common stock, par value $.001, 100,000,000 shares authorized; 22,515,997 and 22,469,413 shares issued; 16,066,404 and 16,633,425 shares outstanding, as of December 31, 2017 and 2016, respectively	23	22
Treasury stock, at cost, 6,449,593 and 5,835,988 shares at December 31, 2017 and 2016, respectively	(605,655)	(517,803)
Additional paid in capital	253,840	238,236
Accumulated other comprehensive loss, net	(2,840)	(230)
Retained earnings	902,579	753,397
TOTAL EQUITY	547,947	473,622
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 2,180,157	$ 1,671,576

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Expendable parts, supplies and fuel, reserve	$ 13,756	$ 7,205
Property, Plant, and Equipment, Owned, Accumulated Depreciation	276,548	466,151
Inventory Valuation Reserves	13,800	7,200
Variable Interest Entity, Consolidated, Carrying Amount, Assets	112,750	0
Accumulated Amortization of Other Deferred Costs	8,218	1,510
Debt Issuance Costs, Gross, Current	2,298	1,868
Variable Interest Entity, Consolidated, Liabilities, Noncurrent	92,424	0
Variable Interest Entity, Consolidated, Liabilities, Current	8,935	0
Debt Issuance Cost, Gross, Noncurrent	$ 3,812	$ 3,035
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	22,515,997	22,469,413
Common stock, shares outstanding	16,066,404	16,633,425
Treasury stock, shares	6,449,593	5,835,988

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING REVENUE:
Scheduled service revenue	$ 818,136	$ 753,414	$ 735,563
Ancillary revenue:
Air-related charges	546,476	499,542	434,317
Third party products	52,707	44,940	40,177
Total ancillary revenue	599,183	544,482	474,494
Fixed fee contract revenue	48,708	31,972	19,747
Other revenue	37,751	32,963	32,384
Total operating revenue	1,503,778	1,362,831	1,262,188
OPERATING EXPENSES:
Aircraft fuel	343,333	257,332	278,394
Salary and benefits	371,599	291,974	229,802
Station operations	142,581	124,052	102,294
Maintenance and repairs	113,481	111,070	92,575
Depreciation and amortization	121,713	105,216	98,097
Sales and marketing	52,711	20,527	21,349
Aircraft lease rentals	3,098	924	2,326
Other	92,840	81,178	65,649
Special charge	35,253	0	0
Total operating expenses	1,276,609	992,273	890,486
OPERATING INCOME	227,169	370,558	371,702
OTHER (INCOME) EXPENSE:
Interest income	(5,808)	(3,010)	(1,452)
Interest expense	(38,990)	(28,836)	(26,510)
Other, net	(1,559)	(1,226)	(75)
Total other expense	31,623	24,600	24,983
INCOME BEFORE INCOME TAXES	195,546	345,958	346,719
PROVISION FOR INCOME TAXES	644	126,368	126,389
NET INCOME	194,902	219,590	220,330
Net loss attributable to noncontrolling interest	0	0	(44)
NET INCOME ATTRIBUTABLE TO ALLEGIANT TRAVEL COMPANY	$ 194,902	$ 219,590	$ 220,374
Earnings per share to common shareholders:
Basic (in Dollars per share)	$ 11.94	$ 13.23	$ 12.97
Diluted (in Dollars per share)	$ 11.93	$ 13.21	$ 12.94
Shares used for computation:
Basic (in Shares)	16,073,000	16,465,000	16,923,000
Diluted (in Shares)	16,095,000	16,489,000	16,962,000
Cash dividends declared per share:	$ 2.80	$ 2.40	$ 2.75

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 194,902	$ 219,590	$ 220,330
Other comprehensive (loss) income:
Change in available for sale securities, net of tax	49	318	(185)
Foreign currency translation adjustments	(681)	88	226
Change in derivatives, net of tax	(871)	(424)	874
Reclassification of derivative gains into Other revenue	(1,107)	(1,046)	(1,292)
Total other comprehensive loss	(2,610)	(1,064)	(377)
TOTAL COMPREHENSIVE INCOME	192,292	218,526	219,953
Comprehensive loss attributable to noncontrolling interest	0	0	(44)
COMPREHENSIVE INCOME ATTRIBUTABLE TO ALLEGIANT TRAVEL COMPANY	$ 192,292	$ 218,526	$ 219,997

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock	Parent	Noncontrolling Interest
Common stock, shares issued		17,413,000
Common Stock, Value, Issued		$ 22
Additional paid in capital			$ 221,257
Accumulated Other Comprehensive Income (Loss), Net of Tax				$ 1,211
Retained Earnings (Accumulated Deficit)					$ 395,783
Treasury Stock, Value						$ (325,396)
TOTAL EQUITY							$ 292,877
Stockholders' Equity Attributable to Noncontrolling Interest								$ 1,188
Balance at at Dec. 31, 2014	$ 294,065
Balance at at Dec. 31, 2015	350,005
Issuance of restricted stock		40,000
Exercises of stock options and stock-settled SARs (Shares)		37,000
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	7,307		7,307				7,307
Tax benefit from stock based compensation	3,865		3,865				3,865
Gain (Loss) on Disposition of Stock in Subsidiary	$ (702)		(3,484)		3,926		442	(1,144)
Stock Repurchased During Period, Shares	(682,003)	(695,000)
Treasury Stock, Value, Acquired, Cost Method	$ (129,455)					(129,455)	(129,455)
Stock Issued During Period, Shares, Employee Stock Purchase Plans	8,306	8,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 1,436					1,436	1,436
Dividends, Cash	(46,464)				(46,464)		(46,464)
Unrealized gain on short-term investments, net of tax	(377)			(377)			(377)
Net income (loss)	220,330				220,374		220,374	(44)
Common stock, shares issued		16,803,000
Common Stock, Value, Issued		$ 22
Additional paid in capital			228,945
Accumulated Other Comprehensive Income (Loss), Net of Tax				834
Retained Earnings (Accumulated Deficit)					573,619
Treasury Stock, Value						(453,415)
TOTAL EQUITY							350,005
Stockholders' Equity Attributable to Noncontrolling Interest								0
Balance at at Dec. 31, 2016	473,622
Issuance of restricted stock		214,000
Exercises of stock options and stock-settled SARs (Shares)		5,000
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	9,291		9,291				9,291
Stock Repurchased During Period, Shares		(402,000)
Treasury Stock, Value, Acquired, Cost Method	$ (66,371)					(66,371)	(66,371)
Stock Issued During Period, Shares, Employee Stock Purchase Plans	13,400	13,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 1,983					1,983	1,983
Dividends, Cash	(39,812)				(39,812)		(39,812)
Unrealized gain on short-term investments, net of tax	1,064			1,064			1,064
Net income (loss)	$ 219,590				219,590		219,590
Common stock, shares issued	16,633,425	16,633,000
Common Stock, Value, Issued	$ 22	$ 22
Additional paid in capital	238,236		238,236
Accumulated Other Comprehensive Income (Loss), Net of Tax	(230)			(230)
Retained Earnings (Accumulated Deficit)	753,397				753,397
Treasury Stock, Value	(517,803)					(517,803)
TOTAL EQUITY	473,622						473,622
Balance at at Dec. 31, 2017	547,947
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures		31,000
Stock Issued During Period, Value, Other	1	$ 1					1
Exercises of stock options and stock-settled SARs (Shares)		16,000
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	15,604		15,604				15,604
Stock Repurchased During Period, Shares		(632,000)
Treasury Stock, Value, Acquired, Cost Method	$ (90,457)					90,457	90,457
Stock Issued During Period, Shares, Employee Stock Purchase Plans	18,498	18,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 2,605					2,605	2,605
Dividends, Cash	(45,720)				(45,720)		(45,720)
Unrealized gain on short-term investments, net of tax	(2,610)			(2,610)			(2,610)
Net income (loss)	$ 194,902				194,902		194,902
Common stock, shares issued	16,066,404	16,066,000
Common Stock, Value, Issued	$ 23	$ 23
Additional paid in capital	253,840		$ 253,840
Accumulated Other Comprehensive Income (Loss), Net of Tax	(2,840)			$ (2,840)
Retained Earnings (Accumulated Deficit)	902,579				$ 902,579
Treasury Stock, Value	(605,655)					$ 605,655
TOTAL EQUITY	$ 547,947						$ 547,947
Stockholders' Equity Attributable to Noncontrolling Interest								$ 0

Consolidated Statements of Sto7

Consolidated Statements of Stockholders' Equity (Parentheticals) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Cash dividends (per Share)	$ 2.80	$ 2.40	$ 2.75

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dividends, Cash	$ 45,720	$ 39,812	$ 46,464
OPERATING ACTIVITIES:
Net income	194,902	219,590	220,330
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	121,713	105,216	98,097
Loss on aircraft and other equipment disposals	9,334	4,981	4,630
Special charge	35,253	0	0
Provision for obsolescence of expendable parts, supplies and fuel	4,576	2,598	1,604
Amortization of deferred financing costs	1,357	1,688	1,099
Share-based compensation expense	13,856	9,389	10,474
Deferred income taxes	42,473	29,846	8,979
Excess tax benefits from share-based compensation	0	0	(3,865)
Changes in certain assets and liabilities:
(Increase) decrease in accounts receivable	(30,568)	(18,201)	(1,693)
(Increase) decrease in prepaid expenses	(7,654)	1,999	6,030
Increase (decrease) in accounts payable	4,798	9,209	(6,431)
Increase (decrease) in accrued liabilities	9,251	7,596	14,673
Increase (decrease) in air traffic liability	16,183	(4,135)	12,821
Change in deferred major maintenance	(20,687)	(18,857)	0
Other, net	(3,656)	(4,058)	(1,381)
Net cash provided by operating activities	391,131	346,861	365,367
INVESTING ACTIVITIES:
Purchase of investment securities	(363,300)	(444,532)	(357,546)
Proceeds from maturities of investment securities	319,915	361,082	373,816
Aircraft pre-delivery deposits	(11,810)	(125,434)	0
Purchase of property and equipment, including capitalized interest	(568,439)	(199,743)	(252,686)
Other investing activities	5,115	6,790	2,198
Net cash used in investing activities	(618,519)	(401,837)	(234,218)
FINANCING ACTIVITIES:
Cash dividends paid to shareholders	(45,720)	(67,540)	(62,439)
Excess tax benefits from share-based compensation	0	0	3,865
Proceeds from the issuance of debt	497,540	321,160	121,000
Repurchase of common stock	(90,457)	(66,371)	(129,455)
Principal payments on debt	(138,858)	(154,080)	(67,930)
Other financing activities	(379)	(594)	1,312
Net cash provided by (used in) financing activities	222,126	32,575	(133,647)
Net change in cash and cash equivalents	(5,262)	(22,401)	(2,498)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	64,711	87,112	89,610
CASH AND CASH EQUIVALENTS AT END OF PERIOD	59,449	64,711	87,112
Cash payments for:
Interest paid, net of amount capitalized	35,998	26,454	26,307
Income taxes, net of refunds	(17,954)	110,612	111,399
Parent
Dividends, Cash	45,720	39,812	46,464
OPERATING ACTIVITIES:
Net income	$ 194,902	$ 219,590	$ 220,374

Organization and Business of Co

Organization and Business of Company (Notes)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Business of Company	Organization and Business of Company Allegiant Travel Company (the “Company”) is a leisure travel company focused on providing travel services and products to residents of under-served cities in the United States. The Company operates a low-cost passenger airline which sells air transportation both on a stand-alone basis and bundled with the sale of air-related and third party services and products. The Company also provides air transportation under fixed fee flying arrangements, and generates aircraft and engine lease revenue. Scheduled service and fixed fee air transportation services have similar operating margins, economic characteristics, production processes (check-in, baggage handling and flight services) which target the same class of customers, and are subject to the same regulatory environment. As a result, the Company believes it operates in one reportable segment and does not separately track expenses for scheduled service and fixed fee air transportation services.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements include the accounts of Allegiant Travel Company (the "Company") and its wholly-owned operating subsidiaries. The Company has no independent assets or operations, and all guarantees of the Company's publicly held debt are full and unconditional and joint and several. Any subsidiaries of the parent company other than the subsidiary guarantors are minor. The Company's investments in unconsolidated affiliates, which are 50 percent or less owned, are accounted for under the equity and cost method. All intercompany balances and transactions have been eliminated. Certain reclassifications have been made to the prior period amounts to conform to current year presentation. Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities, at the date of the financial statements based on events and transactions occurring during the periods reported, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates. Cash and Cash Equivalents Cash and cash equivalents include investments and interest bearing instruments with maturities of three months or less at the balance sheet date. Such investments are carried at cost which approximates fair value. Restricted Cash Restricted cash represents escrowed funds under fixed fee contracts, and cash collateral against letters of credit required by hotel properties for guaranteed room availability, airports and certain other parties. Restricted cash at December 31, 2017 and 2016 was $11.2 million and $11.6 million , respectively. Accounts Receivable Accounts receivable are carried at face amount which approximates fair value. They consist primarily of amounts due from credit card companies associated with the sale of tickets for future travel, commission amounts due from Enterprise Holdings Inc., based on terms in the rental car provider agreement, income tax receivables, and amounts due related to fixed fee charter agreements. If deemed necessary, the Company records charges to its allowance for doubtful accounts for amounts not expected to be collected. The allowance for doubtful accounts was zero as of December 31, 2017 and 2016 . The Company also had an outstanding receivable from a third party as of December 31, 2017 , for which $6.3 million is due more than one year after the balance sheet date and is classified with the Company's other assets. Short-term and Long-term Investments The Company’s investments in marketable securities are classified as available-for-sale and are reported at fair value with the net unrealized gain or (loss) reported as a component of accumulated other comprehensive income in shareholders’ equity. Investment securities are classified as cash equivalents, short-term investments and long-term investments based on maturity date as of the balance sheet date. Cash equivalents have maturities of three months or less, short-term investments have maturities of greater than three months but equal to or less than one year, and long-term investments are those with a maturity date greater than one year. As of December 31, 2017 , the Company’s long-term investments consisted of corporate debt securities, federal agency debt securities, US Treasury Bonds, and municipal debt securities with contractual maturities of less than 24 months. The amortized cost of investment securities sold is determined by the specific identification method with any realized gains or losses reflected in other (income) expense. The Company had minimal realized losses during the years ended December 31, 2017 , 2016 , and 2015 . The Company believes unrealized losses related to debt securities are not other-than-temporary and does not intend to sell these securities prior to amortized cost recoverability. The Company attempts to minimize its concentration risk with regard to its cash, cash equivalents, and investment portfolio. This is accomplished by diversifying and limiting amounts among different counterparties, the type of investment, and the amount invested in any individual security, commercial paper, or money market fund. Expendable Parts, Supplies and Fuel, Net Expendable parts, supplies and fuel inventories are valued at cost using the first-in, first-out method. Such inventories are charged to expense as they are used in operations. An obsolescence allowance for expendable parts and supplies is based on the remaining useful lives of the corresponding fleet type and salvage values. The allowance for expendable parts and supplies was $13.8 million and $7.2 million at December 31, 2017 and 2016 , respectively. Rotable aircraft parts inventories are included in property and equipment. Software Capitalization The Company capitalizes certain internal and external costs related to the acquisition and development of computer software during the application development stage of projects. The Company amortizes these capitalized costs using the straight-line method over the estimated useful life of the software, which typically ranges from three to five years. The Company had unamortized computer software development costs of $41.0 million and $40.4 million as of December 31, 2017 and 2016 , respectively. Amortization expense related to computer software was $15.9 million , $13.3 million and $10.0 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Costs incurred during the preliminary and post-implementation stages are expensed as incurred. Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over their estimated useful lives less an estimated salvage value. The estimated useful lives of the principal asset classes are shown below. As of December 31, 2017 , our MD-80 fleet has been fully impaired and has no remaining depreciable book value. Aircraft, engines and related rotable parts 10-25 years Buildings 25 years Equipment and leasehold improvements 3-7 years Computer hardware and software 3-5 years In estimating the useful lives and residual values of aircraft, the Company primarily has relied upon actual experience with the same or similar aircraft types, current and projected future market information, and recommendations from other industry sources. Subsequent revisions to these estimates could be caused by changing market prices of the Company’s aircraft, changes in utilization of the aircraft, and other fleet events. These estimates are evaluated each reporting period and adjusted if necessary. Changes in the estimate for useful lives or residual values of the Company’s property and equipment could result in an acceleration of depreciation expense associated with the change in estimate. Payments required to be made in advance of aircraft delivery are qualifying assets and interest attributable to these payments is capitalized as part of the cost of the related asset until the aircraft has been delivered and is ready to enter revenue service. Interest is capitalized at the Company’s weighted average borrowing rate and depreciated over the estimated useful life of the asset. Capitalized interest for 2017 was $3.2 million and $1.8 million in 2016. Aircraft Maintenance and Repair Costs The Company accounts for non-major maintenance and repair costs incurred under the direct expense method. Under this method, maintenance and repair costs for owned and leased aircraft are charged to operating expenses as incurred. Maintenance and repair costs includes all parts, materials, line maintenance, and non-major maintenance activities required to maintain the Company's multiple fleet types. The Company accounts for major maintenance costs of its MD-80 airframes and the related JT8D-219 engines using the direct expense method. Under this method, major maintenance costs are charged to expense as incurred. The Company accounts for major maintenance costs of its Airbus airframes and the related CFM engines using the deferral method. Under this method, the Company capitalizes the cost of major maintenance events, which are amortized as a component of depreciation and amortization expense, over the estimated period until the next scheduled major maintenance event. During 2017 and 2016, the Company deferred $20.7 million and $18.9 million of costs for major maintenance with associated amortization expense charged to depreciation and amortization of $6.7 million and $1.5 million , respectively. Measurement of Impairment of Long-Lived Assets The Company records impairment losses on long-lived assets used in operations, consisting principally of property and equipment, when events or changes in circumstances indicate, in management’s judgment, that the assets might be impaired, and the undiscounted future cash flows estimated to be generated by those assets are less than the carrying amount of those assets. In making these determinations, the Company utilizes certain assumptions, including, but not limited to: (i) estimated fair value of the assets; and (ii) estimated future cash flows expected to be generated by these assets, which are based on additional assumptions such as asset utilization, length of service for which the asset will be used in operations, and estimated salvage values. For the year ended December 31, 2017 , the Company recorded a non-cash impairment charge of $35.3 million on its fleet of MD-80 aircraft, engines, and related assets, as a result of its review of fleet value. This represents a full impairment of these assets, and as such, these assets have no remaining book value. The Company analyzed many factors, including the accelerated retirement dates of the MD-80 fleet, a reduction in aircraft utilization due to the continued induction of Airbus A320 series aircraft, and the significantly decreased level of demand in the secondary market for MD-80 aircraft, spare engines, and parts. For the years ended December 31, 2017, 2016 and 2015 , the Company incurred impairment losses related to various aircraft parts, of $1.3 million , $3.0 million , and $1.1 million , respectively and classified within Other operating expense. Revenue Recognition Scheduled service revenue Scheduled service revenue consists of passenger revenue generated from nonstop flights in the Company’s route network, recognized either when the travel-related service or transportation is provided or when the itinerary expires unused. Nonrefundable scheduled itineraries expire on the date of the intended flight, unless the date is extended by notification from the customer in advance. Itineraries sold for transportation not yet used, as well as unexpired credits, are included in air traffic liability. Various taxes and fees, assessed on the sale of tickets to customers, are collected by the Company serving as an agent, and remitted to taxing authorities. These taxes and fees are not included as revenue in the Company’s consolidated statements of income and are recorded as a liability until remitted to the appropriate taxing authority. Ancillary air-related revenue Ancillary air-related revenue is generated from fees paid by ticketed passengers and consists of baggage fees, the use of the Company’s website to purchase scheduled service transportation, advance seat assignments, and other services. Revenues from air-related charges are recognized when the transportation is provided if the product is not deemed distinct of the original ticket sale. Change and cancellation fees for nonrefundable itineraries are air-related charges deemed distinct of the original ticket sale, and are recognized as revenue when the fee is incurred by the customer. Ancillary third party revenue Ancillary revenue is also generated from the sale of third party products such as hotel rooms, rental cars and ticket attractions. Revenue from the sale of third party products is recognized at the time the product is utilized, such as the time a purchased hotel room is occupied. The Company follows accounting standards for determining whether it is a principal or an agent in revenue arrangements to determine the amount of revenue to be recognized for each element of a bundled sale involving air-related charges and third party products in addition to airfare. Revenue from the sale of third party products is recorded net (treatment as an agent) of amounts paid to wholesale providers, travel agent commissions, and transaction costs. Fixed fee contract revenue Fixed fee contract revenue consists of agreements to provide charter service on a year-round and ad hoc basis. Fixed fee contract revenue is recognized when the transportation is provided. Other revenue Other revenue is generated from leased aircraft, engines, and other miscellaneous sources. Lease revenue is recognized ratably over the lease term. Affinity Credit Card Program The Allegiant World Mastercard® is issued by Bank of America through which arrangement points are sold and consideration is received under an agreement with a seven year scheduled duration expiring in 2023. Under this arrangement, the Company identified the following deliverables: travel points to be awarded (the travel component), use of the Company’s brand and access to its member lists, and certain other advertising and marketing elements (collectively the marketing component). Applying guidance under Accounting Standards Update (“ASU”) 2009-13 - Revenue Recognition (Topic 605): Multiple-Deliverable Revenue Arrangements, each of these deliverables is accounted for separately and allocation of the consideration from the agreement is determined based on the relative selling price of each deliverable. The Company applied a level of management judgment and estimation in determining the best estimate of selling price for each deliverable by considering multiple inputs and methods including, but not limited to, the redemption value of points awarded, discounted cash flows, brand value, volume discounts, published selling prices, number of points to be awarded and number of points to be redeemed. The travel component is deferred based on its relative selling price and is recognized into scheduled service revenue when the points are redeemed by cardholders. The marketing component is considered earned in the period in which points are sold and is therefore recognized into third party products revenue in the same period. Advertising Costs Advertising costs are charged to expense in the period incurred. Advertising expense was $20.9 million , $13.6 million and $12.7 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Earnings per Share Basic and diluted earnings per share are computed pursuant to the two-class method as opposed to the treasury method. Under this method, the Company attributes net income to two classes, common stock and unvested restricted stock awards. Unvested restricted stock awards granted to employees under the Company’s Long-Term Incentive Plan are considered participating securities because they receive non-forfeitable rights to cash dividends at the same rate as common stock. Diluted net income per share is calculated using the more dilutive of two methods. Under both methods, the exercise of employee stock options is assumed using the treasury stock method. The assumption of vesting of restricted stock, however, differs as described below: 1. Assume vesting of restricted stock using the treasury stock method. 2. Assume unvested restricted stock awards are not vested, and allocate earnings to common shares and unvested restricted stock awards using the two-class method. For the years ended December 31, 2017 , 2016 and 2015 , the second method above was used in the computation because it was more dilutive than the first method. The following table sets forth the computation of net income per share on a basic and diluted basis for the periods indicated (in thousands, except per share amounts): Year ended December 31, 2017 2016 2015 Basic: Net income $ 194,902 $ 219,590 $ 220,374 Less net income allocated to participating securities (2,917 ) (1,748 ) (961 ) Net income attributable to common stock $ 191,985 $ 217,842 $ 219,413 Net income per share, basic $ 11.94 $ 13.23 $ 12.97 Weighted-average shares outstanding 16,073 16,465 16,923 Diluted: Net income $ 194,902 $ 219,590 $ 220,374 Less net income allocated to participating securities (2,914 ) (1,746 ) (958 ) Net income attributable to common stock $ 191,988 $ 217,844 $ 219,416 Net income per share, diluted $ 11.93 $ 13.21 $ 12.94 Weighted-average shares outstanding 16,073 16,465 16,923 Dilutive effect of stock options and restricted stock 74 42 69 Adjusted weighted-average shares outstanding under treasury stock method 16,147 16,507 16,992 Participating securities excluded under two-class method (52 ) (18 ) (30 ) Adjusted weighted-average shares outstanding under two-class method 16,095 16,489 16,962 Stock awards outstanding of 5,752 ; 1,918 ; and 28,789 shares for 2017 , 2016 , and 2015 , respectively, were excluded from the computation of diluted earnings per share as they were antidilutive. Share-Based Compensation The Company accounts for share-based compensation in accordance with accounting standards which require the compensation cost related to share-based payment transactions be recognized in the Company’s consolidated statements of income. The cost is measured at the grant date, based on the calculated fair value of the award using the Black-Scholes option pricing model for cash-settled SARs, and is remeasured monthly for cash-settled SARs. Fair value is based on the closing price of the Company’s stock on the grant date for restricted stock awards. The cost is recognized as an expense over the requisite service period (the vesting period of the award) which is generally three years. Forfeiture rates for each type of award are estimated at time of grant. The Company’s share-based employee compensation plan is more fully discussed in Note 11- Employee Benefit Plans. Income Taxes The Company recognizes deferred income taxes based on the asset and liability method required by accounting standards. Deferred tax assets and liabilities are determined based on the timing differences between book basis for financial reporting purposes and tax basis of the asset and liability and measured using the enacted tax rates. A valuation allowance for deferred tax assets is provided if it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company determines the net non-current deferred tax assets or liabilities separately for federal, state, foreign and other local jurisdictions. The Company’s income tax returns are subject to examination by the Internal Revenue Service (“IRS”) and other tax authorities in the jurisdictions where the Company operates. The Company assesses potentially unfavorable outcomes of such examinations based on the criteria set forth in uncertain tax position accounting standards. The accounting standards prescribe a minimum recognition threshold a tax position is required to meet before being recognized in the financial statements. Accounting standards for income taxes utilize a two-step approach for evaluating tax positions. Recognition (Step I) occurs when the Company concludes that a tax position, based on its technical merits, is more likely than not to be sustained upon examination. Measurement (Step II) is only addressed if the position is deemed to be more likely than not to be sustained. Under Step II, the tax benefit is measured as the largest amount of benefit that is greater than 50 percent likely of being realized upon settlement. The tax positions failing to qualify for initial recognition are recognized in the first subsequent interim period they meet the “more likely than not” standard. If it is subsequently determined that a previously recognized tax position no longer meets the “more likely than not” standard, it is required that the tax position be derecognized. As applicable, the Company will recognize accrued penalties and interest related to unrecognized tax benefits in the provision for income taxes. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU 2014-09, "Revenue from Contracts with Customers (Topic 606)" intended to create a unified model to determine when and how revenue is recognized. Under this ASU and subsequently issued amendments, the core principle is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration for which the entity expects to be entitled in exchange for those goods or services. The Company will adopt this standard using the full-retrospective approach on January 1, 2018. Under the new standard, revenue for certain air-related ancillary fees that are directly related to ticket revenue, such as seat fees and baggage fees, will no longer be considered distinct performance obligations separate from passenger travel and will be reclassified into scheduled service revenue. The amounts expected to be reclassified from air-related charges into scheduled service revenue will be between approximately $536 million and $546 million for 2017 and between $490 million and $500 million for 2016. In addition, certain fees previously recognized when incurred by the customer, will be deferred and recognized as revenue when air travel is provided and reclassified into scheduled service revenue, as well as reclassification of certain expense items to scheduled service revenue. Although the Company is in the process of finalizing analysis needed to recast prior periods, it is believed that adoption will not have a material effect on earnings. In January 2016, the FASB issued ASU 2016-01, a standard which includes several changes to financial instruments, including the elimination of the available-for-sale classification of equity investments, requiring those with readily determinable fair values to be measured at fair value with changes in fair value recognized in net income. The standard is effective for annual and interim periods beginning after December 15, 2017, and the Company will adopt it effective January 1, 2018. The Company does not expect the adoption will have a material impact on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02 related to leases. This standard will require leases with durations greater than twelve months to be recognized on the balance sheet as a lease liability and a corresponding right-of-use asset, and is effective for interim and annual reporting periods beginning after December 15, 2018 with early adoption permitted. The Company has not completed the assessment of this new standard. The Company believes adoption will have a significant impact on its consolidated balance sheets but is not expected to significantly change the recognition or measurement of associated expense within the consolidated statements of income or cash flows. In August 2016, the FASB issued ASU 2016-15, which amends the guidance in Accounting Standards Codification ("ASC") 230 on the classification of certain cash receipts and payments in the statement of cash flows. The primary purpose of the ASU is to reduce the diversity in practice that has resulted from the lack of consistency on this topic. The standard is effective for annual and interim periods beginning after December 15, 2017, and the Company will adopt it effective January 1, 2018. Significant classification modifications are not expected as a result of adoption. In November 2016, the FASB issued ASU 2016-18 which clarifies the presentation of restricted cash and restricted cash equivalents on the statement of cash flows. This ASU requires that the change in total cash, cash at beginning of period and cash at end of period on the statement of cash flows include restricted cash and restricted cash equivalents and also requires companies reporting cash and restricted cash separately on the balance sheet to reconcile those amounts to the statement of cash flows. The standard is to be applied retrospectively and is effective for annual and interim periods beginning after December 15, 2017. The Company will adopt it effective January 1, 2018 and does not expect the adoption will have a material impact on its consolidated financial statements.

Property and Equipment (Notes)

Property and Equipment (Notes)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment Disclosure	Property and Equipment Property and equipment consisted of the following (in thousands): As of December 31, 2017 As of December 31, 2016 Flight equipment, including pre-delivery deposits $ 1,539,433 $ 1,377,829 Computer hardware and software 123,675 101,850 Other property and equipment 125,855 81,786 Total property and equipment 1,788,963 1,561,465 Less accumulated depreciation and amortization (276,548 ) (466,151 ) Property and equipment, net $ 1,512,415 $ 1,095,314 As of December 31, 2017 , the Company had firm commitments to purchase 16 new and used Airbus A320 series aircraft which are expected to be delivered between 2018 and 2020. In addition, the Company expects to take delivery, in 2018, of its remaining 11 owned Airbus A320 series aircraft on lease to a European carrier. As of December 31, 2017 , Other property and equipment included $20.8 million in land acquired for the development of Sunseeker Resorts.

Accrued Liabilities (Notes)

Accrued Liabilities (Notes)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Accounts Payable and Accrued Liabilities Disclosure	Accrued Liabilities Accrued liabilities consisted of the following (in thousands): As of December 31, 2017 As of December 31, 2016 Salaries, wages and benefits $ 35,516 $ 38,860 Interest 13,326 11,891 Station expenses 12,026 14,799 Passenger fees 11,420 11,200 Property taxes 7,851 6,613 Maintenance and repairs 5,481 4,953 Advertising accruals 4,154 676 Passenger taxes 447 394 Other accruals 14,906 7,275 Total accrued liabilities $ 105,127 $ 96,661 As of December 31, 2017 , the balance in Other accruals is related to various accruals, including $5.0 million in information technology related accruals.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt Long-term debt consisted of the following (in thousands): As of December 31, 2017 As of December 31, 2016 Fixed-rate notes payable due through 2020 $ 465,462 $ 465,748 Variable-rate notes payable due through 2027 699,430 342,526 Total long-term debt, net of related costs 1,164,892 808,274 Less current maturities, net of related costs 214,761 86,226 Long-term debt, net of current maturities and related costs $ 950,131 $ 722,048 Weighted average fixed-interest rate 5.4 % 5.4 % Weighted average variable-interest rate 3.3 % 3.2 % Maturities of long-term debt as of December 31, 2017 , for the next five years and thereafter, in the aggregate, are: 2018 - $214.8 million ; 2019 - $561.6 million ; 2020 - $95.2 million ; 2021 - $68.0 million ; 2022 - $41.5 million ; and $183.8 million thereafter. Total long-term debt is presented net of related costs of $6.1 million and $4.9 million at December 31, 2017 and 2016, respectively. Secured Debt As of December 31, 2017 and 2016, respectively, the Company had $699.4 million and $342.5 million of variable rate debt secured by 57 and 34 Airbus A320 series aircraft. Each note bears interest at a floating rate based on LIBOR and most are payable in quarterly installments over five or ten year terms. These amounts include debt and secured aircraft under the Company's variable interest entity ("VIE") and revolving credit facility agreements, which are discussed in further detail below. As of December 31, 2017 and 2016, the Company had $15.7 million and $16.2 million , respectively, of fixed rate debt secured by real estate owned by the Company. These notes bear interest at a fixed rate and are payable in monthly installments over five year terms, with one loan maturing in 2018 and one loan maturing in 2020. Consolidated Variable Interest Entity The Company evaluates ownership, contractual lease arrangements and other interest in entities to determine if they are variable interest entities ("VIEs") based on the nature and extent of those interests. These evaluations are complex and involve judgment and the use of estimates and assumptions based on available historical information and management’s judgment, among other factors. The Company consolidates a VIE when, among other criteria, it has the power to direct the activities that most significantly impact the VIE’s economic performance as well as the obligation to absorb losses or the right to receive benefits of the VIE, thus making the Company the primary beneficiary of the VIE. In December 2017, the Company entered into an agreement with a trust to finance three Airbus A320 aircraft, under which the aircraft serve as collateral for the financing. The trust was funded on inception by a $102.0 million long-term debt agreement entered into by the trust. These borrowings bear interest at a floating rate based on LIBOR and will be payable in quarterly installments through December 2027. As this transaction is a common control transaction, the Company, as the primary beneficiary, has measured and recorded the assets and liabilities at their carrying values, which were $112.8 million and $102.0 million , respectively, as of December 31, 2017 . The Company did not have a variable interest in any entity in 2016. Senior Secured Revolving Credit Facility In 2015, the Company, through a wholly owned subsidiary, entered into a senior secured revolving credit facility under which it is able to borrow up to $56.0 million . As of December 31, 2017 , the balance under this facility was $41.3 million , net of related costs, with five Airbus aircraft included in the collateral pool. The notes will mature in December 2018. The facility may be extended for an additional one-year period, to 2019, at the lender’s option. Any notes under the facility bear interest at a floating rate based on LIBOR. An individual aircraft may remain in the collateral pool for up to two years. General Unsecured Senior Notes In June 2014, the Company completed an offering of $300.0 million aggregate principal amount of senior unsecured obligations (the "Notes") which will mature in July 2019. In December 2016, the Company completed an offering of an additional $150.0 million principal amount of these notes, which were issued at a price of 101.5 percent of the principal amount, plus accrued interest from July 15, 2016. The Notes constitute general unsecured senior obligations of the Company and rank equally in right of payment with all existing and future senior unsecured indebtedness and liabilities (including trade payables) of the Company. The Notes are effectively junior to the Company’s existing and future secured indebtedness. The Notes are guaranteed by all of the Company’s wholly-owned domestic subsidiaries and rank equally in right of payment with all existing and future unsecured indebtedness and liabilities (including trade payables) of the Company’s guarantor subsidiaries, but effectively junior to the guarantors’ existing and future secured indebtedness. 5.5 percent per year, payable in cash semi-annually, on January 15 and July 15 of each year, and will mature on July 15, 2019. The indenture pursuant to which the Notes were issued includes operating and financial restrictions on the Company. These restrictions limit or restrict, among other things, the Company’s ability and the ability of its restricted subsidiaries to (i) incur additional indebtedness; (ii) incur liens; (iii) make restricted payments (including paying dividends on, redeeming, repurchasing or retiring capital stock); (iv) make investments; and (v) consolidate, merge or sell all or substantially all of its assets. These covenants are subject to various exceptions and qualifications under the terms of the indenture. For the four quarters ended December 31, 2017 , the Company exceeded the consolidated total leverage ratio limit, which could affect the ability to make restricted payments in future periods after exhaustion of various exceptions. The calculation is made on a quarterly basis based on the trailing 12 months.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	Shareholders’ Equity The Company is authorized by its Board of Directors to acquire the Company’s stock through open market and private purchases under its share repurchase program. As repurchase authority is used, the Board of Directors has, to date, authorized additional expenditures for share repurchases. Share repurchases consisted of the following during the periods indicated: Twelve Months Ended December 31, 2017 2016 2015 Shares repurchased (1) 604,497 391,972 682,003 Average price per share $ 142.66 $ 164.99 $ 186.43 Total (in thousands) 86,240 64,673 127,147 (1) Share amounts shown above include only open market repurchases and do not include shares withheld from employees for tax withholding obligations related to restricted stock vestings, which were 27,606 , 10,103 , and 12,682 shares for 2017, 2016 and 2015, respectively. As of December 31, 2017 , the Company had $100.0 million in unused share repurchase authority remaining under the Board approved program. During 2017, the Board declared, and the Company paid, total quarterly cash dividends of $2.80 per share for a total of $45.7 million . During 2016, the Board declared, and the Company paid, total quarterly cash dividends of $2.40 per share for a total of $39.8 million . During 2015, the Board declared, and the Company paid, total quarterly cash dividends of $1.10 per share for a total of $18.7 million . Prior to year-end 2015, the Board declared a special cash dividend of $1.65 per share on outstanding common stock payable to shareholders of record on December 18, 2015. On January 8, 2016, the Company paid $27.7 million to these shareholders.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Investments The Company measures certain financial assets and liabilities at fair value on a recurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Accounting standards pertaining to fair value measurements establish a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1 - Defined as observable inputs such as quoted prices in active markets for identical assets or liabilities Level 2 - Defined as inputs other than Level 1 inputs that are either directly or indirectly observable Level 3 - Defined as unobservable inputs for which little or no market data exists, therefore requiring an entity to develop its own assumptions The Company uses the market approach valuation technique to determine fair value for investment securities. The assets classified as Level 1 consist of money market funds for which original cost approximates fair value. The assets classified as Level 2 consist of commercial paper, municipal debt securities, federal agency debt securities, corporate debt securities, and US treasury bonds, which are valued using quoted market prices or alternative pricing sources including transactions involving identical or comparable assets and models utilizing market observable inputs. The Company has no investment securities classified as Level 3. For those assets classified as Level 2 that are not in active markets, the Company obtains fair value from pricing sources using quoted market prices for identical or comparable instruments, and uses pricing models which include all significant observable inputs: maturity dates, issue dates, settlement dates, benchmark yields, reported trades, broker-dealer quotes, issue spreads, benchmark securities, bids, offers and other market related data. These inputs are observable or can be derived from, or corroborated by, observable market data for substantially the full term of the asset. The fair value of the Company's foreign currency derivative instrument is determined using standard valuation models. The significant inputs used in these models are readily available in public markets or can be derived from observable market transactions and therefore have been classified as Level 2. Inputs used in these standard valuation models for derivative instruments include the applicable exchange and interest rates. Financial instruments measured at fair value on a recurring basis (in thousands): As of As of Description Total Level 1 Level 2 Total Level 1 Level 2 Cash equivalents Commercial paper $ 27,910 $ — $ 27,910 $ — $ — $ — Municipal debt securities 2,782 — 2,782 1,843 — 1,843 Money market funds 1,297 1,297 — 123 123 — Federal agency debt securities — — — 19,399 — 19,399 Total cash equivalents 31,989 1,297 30,692 21,365 123 21,242 Short-term Commercial paper 108,678 — 108,678 108,372 — 108,372 Corporate debt securities 107,878 — 107,878 76,570 — 76,570 Municipal debt securities 101,290 — 101,290 78,826 — 78,826 Federal agency debt securities 31,428 — 31,428 3,895 — 3,895 US Treasury Bonds 3,407 — 3,407 1,606 — 1,606 Total short-term 352,681 — 352,681 269,269 — 269,269 Long-term Corporate debt securities 60,396 — 60,396 25,048 — 25,048 Municipal debt securities 9,405 — 9,405 72,623 — 72,623 Federal agency debt securities 5,775 — 5,775 24,160 — 24,160 US Treasury Bonds 2,994 — 2,994 3,003 — 3,003 Derivative instruments 282 — 282 1,660 — 1,660 Total long-term 78,852 — 78,852 126,494 — 126,494 Total financial instruments $ 463,522 $ 1,297 $ 462,225 $ 417,128 $ 123 $ 417,005 There were no significant transfers between Level 1 and Level 2 assets for the years ended December 31, 2017 or 2016 . Long-term Debt The fair value of the Company’s publicly held long-term debt is determined based on inputs that are readily available in public markets or can be derived from information available in publicly quoted markets; therefore, the Company has categorized its publicly held debt as Level 2. The remaining debt agreements are not publicly held. The Company has determined the estimated fair value of these notes to be Level 3, as certain inputs used to determine the fair value of these agreements are unobservable and, therefore, could be sensitive to changes in inputs. The Company utilizes the discounted cash flow method to estimate the fair value of Level 3 debt. Carrying value and estimated fair value of long-term debt, including current maturities (in thousands): As of December 31, 2017 As of December 31, 2016 Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Level Publicly held debt $ 451,321 $ 462,604 $ 452,179 $ 468,005 2 Non-publicly held debt 719,681 660,065 360,999 340,866 3 Total long-term debt $ 1,171,002 $ 1,122,669 $ 813,178 $ 808,871 Other In the fourth quarter of 2017, the Company recorded a non-cash impairment charge of $35.3 million on its fleet of MD-80 aircraft, engines, and related assets as a result of a recent review of fleet value. The Company concluded that the carrying value of these aircraft and related assets was no longer fully recoverable when compared to the estimated remaining future undiscounted cash flows from these assets. Therefore, an adjustment to their fair value with inputs classified as Level 3 was recorded. Due to the short term nature, carrying amounts of cash, cash equivalents, restricted cash, accounts receivable and accounts payable approximate fair value.

Derivative Instruments (Notes)

Derivative Instruments (Notes)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure	Derivative Instruments In 2014, the Company entered into a foreign currency swap in order to mitigate the foreign currency exchange rate risk associated with the forecasted lease revenue from 12 Airbus A320 series aircraft leased to a European carrier until 2018, at which point the foreign currency swap will conclude. One aircraft has re-delivered to the Company as of December 31, 2017 . The Company uses a cash flow hedge to minimize the variability in cash flows of assets or liabilities of forecasted transactions caused by fluctuations in foreign currency exchange rates. At December 31, 2017 , 2016 and 2015, respectively, the change in fair value recorded in accumulated other comprehensive income was a decrease of $0.9 million and $0.4 million and an increase of $0.9 million . At inception, the Company formally designated and documented this financial instrument as a hedge of a specific underlying exposure, the risk management objective, and the strategy for undertaking the hedge transaction. The Company also assessed whether the financial instrument used in the hedging transactions was effective at offsetting changes in either the fair values or cash flows of the related underlying exposures. This assessment is monitored on at least a quarterly basis, and the change in fair value of any ineffective portion of a financial instrument would be immediately charged against earnings. The Company realized $1.1 million and $1.0 million in net gains from its cash flow hedge in Other revenue from amounts settled under the forward contract in 2017 and 2016, respectively. As of December 31, 2017 , it is expected that approximately $3.0 million will be reclassified from Other comprehensive income into Other revenue within the next 12 months. At December 31, 2017 and 2016 respectively, the fair value of the Company's derivative instrument was $0.3 million and $1.7 million and is reported in the Company's consolidated balance sheet within Deposits and other assets. Refer to Note 7 - Fair Value Measurements for additional information related to the estimated fair value.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Impact of U.S. Federal Income Tax Reform In December, 2017, the “Tax Cuts and Jobs Act” (the “Tax Act”) was signed into law. The significant provisions impacting the Company are as follows: • Effective January 1, 2018, the U.S. corporate income tax rate reduced from 35.0 percent to 21.0 percent; • the Company recognized a one-time tax benefit of $74.7 million due to the remeasurement of deferred tax balances to the new statutory rate; • the Company is eligible to claim 100 percent bonus depreciation on qualified property placed in service from September 28, 2017 through December 31, 2022 - this provision phases out 20 percent annually after 2022 through 2027. ASC 740, Income Taxes, requires companies to recognize the effect of the tax law changes in the period of enactment. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin ("SAB") 118 which allows companies to record provisional amounts during a one-year measurement period in order to complete the accounting for income tax effects of the Tax Act. The Company recognized provisional estimates which may be impacted by the Company’s understanding and application of the Tax Act related to the deductibility of acquired assets, state conformity and additional guidance from federal and state agencies as well as the FASB and the SEC. We are continuing to assess the tax effects of the Tax Act, but do not anticipate that the net impact will be material to our 2018 effective tax rate. The Company is subject to income taxation in the United States, foreign countries and various state jurisdictions in which it operates. In accordance with income tax reporting accounting standards, the Company recognizes tax benefits or expense on the temporary differences between the financial reporting and tax bases of its assets and liabilities. Components of Income before Income Taxes from Continuing Operations The components of income before taxes for domestic and foreign operations consisted of the following (in thousands): Twelve Months Ended December 31, 2017 2016 2015 Domestic $ 176,853 $ 329,818 $ 331,813 Foreign 18,693 16,140 14,906 Total $ 195,546 $ 345,958 $ 346,719 Income Tax Provision/(Benefit) The provision for income taxes is composed of the following (in thousands): Year Ended December 31, 2017 2016 2015 Current: Federal $ (44,385 ) $ 89,014 $ 108,119 State 664 5,204 6,501 Foreign 558 1,262 996 Total current (43,163 ) 95,480 115,616 Deferred: Federal 40,816 27,950 9,458 State 1,962 1,673 125 Foreign 1,029 1,265 1,190 Total deferred 43,807 30,888 10,773 Total income tax provision $ 644 $ 126,368 $ 126,389 Reconciliation of Effective Tax Rate The effective tax rate on income before income taxes differed from the federal statutory income tax rate as follows (in thousands): Year Ended December 31, 2017 2016 2015 Income tax expense at federal statutory rate $ 68,441 $ 121,085 $ 121,352 State income taxes, net of federal income tax benefit 2,723 5,487 4,293 Federal tax reform impact (74,738 ) — — Other 4,218 (204 ) 744 Total income tax expense $ 644 $ 126,368 $ 126,389 Deferred Taxes The major components of the Company’s net deferred tax assets and liabilities are as follows (in thousands): As of December 31, 2017 2016 Deferred tax assets: Accrued vacation $ 690 $ 1,183 Accrued bonus 628 9,340 State taxes 318 2,187 Accrued property taxes 1,573 2,077 Other 3,679 1,910 Stock-based compensation expense 1,983 3,126 Net operating loss 635 — Less: valuation allowance 422 — Total deferred tax assets 9,084 19,823 Deferred tax liabilities: Prepaid expenses 4,275 5,049 Depreciation 118,743 86,981 Foreign deferred 4,569 3,131 Total deferred tax liabilities 127,587 95,161 Net deferred tax liabilities $ 118,503 $ 75,338 Net Operating Loss and Tax Credit Carryforwards At December 31, 2017, the Company recognized $0.2 million of state net operating loss carryforward which will expire between 2032 and 2037. The Company also recognized $0.4 million of foreign net operating loss carryforward which does not expire. As of December 31, 2016, the Company recognized a federal capital loss carryforward which was remeasured to $0.7 million , pursuant to the Tax Act. The carryforward begins to expire in 2021. As of December 31, 2017, the Company also recognized $0.7 million and $0.2 million of foreign tax credit and charitable contribution carryforward balances which will expire in 2028 and 2023, respectively.

Related Party Transactions (Not

Related Party Transactions (Notes)	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions In December 2017, the Company completed a transaction with ISM Connect, LLC ("ISM"), an entity in which the Company's Chairman and CEO owns a majority interest. In exchange for a noncontrolling minority interest in ISM, the Company licensed the right to use certain portions of its internally developed software, but strictly limited to ISM's digital media signage business. The Company retains all rights in the software without restriction. This interest has been valued at $2.3 million and no subsequent transactions with ISM are expected. The Company previously entered into lease agreements for approximately 70,000 and 10,000 square feet of office space in buildings in which the Company’s Chairman and Chief Executive Officer ("CEO") and the Company's President own minority interests as limited partners. The Company exercised its option to terminate the lease for 70,000 square feet of office space effective in May 2015. In connection with the termination of this lease, the Company paid $1.3 million for unamortized expenses in January 2016. Additionally, as of January 2016, payments for the remaining 10,000 square feet of space are no longer being made to a related party entity as the lender has taken ownership of the property. Under the terms of these agreements, the Company made no rent payments to related parties in 2017 or 2016, and made payments of $1.2 million in 2015. Game Plane, LLC, was a wholly owned subsidiary of the Company that produced game shows filmed on Company flights. Prior to its dissolution in 2016, Game Plane, LLC partnered with Alpine Labs, LLC to produce and distribute the shows. The Company’s Chairman and CEO owns a 25 percent interest in, and is on the managing board of, Alpine Labs, LLC. The Company made no payments to Alpine Labs, LLC in 2017 or 2016, and paid $0.4 million in 2015. Entities owned or controlled by the Company's Chairman and CEO have been paid for the building of corporate training content. During 2017, 2016 and 2015, the Company made payments to these entities of $0.2 million , $1.7 million and $2.9 million , respectively, and no further payments are expected. GMS Racing LLC competes in the NASCAR Camping World Truck Series and ARCA Racing Series. The Company's Chairman and CEO owns a controlling interest in GMS Racing LLC. The Company made no sponsorship payments to GMS Racing in either 2016 or 2017, and made payments totaling $2.5 million in 2015. No future payments are expected.

Employee Benefit Plans (Notes)

Employee Benefit Plans (Notes)	12 Months Ended
	Dec. 31, 2017
Employee Benefit Plans [Abstract]
Employee Benefit Plans	Employee Benefit Plans 401(k) Plan The Company has a defined contribution plan covering all eligible employees. Under the plan, employees may contribute up to 90 percent of their eligible annual compensation with the Company making matching contributions on employee deferrals of up to 5 percent of eligible employee wages. In January 2017, the Company increased its matching contributions on pilot deferrals to 10 percent of eligible wages resulting from the pilot collective bargaining agreement. The Company recognized expense under this plan of $14.2 million , $5.8 million and $4.2 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Share-based employee compensation In 2016, the Board of Directors adopted and the shareholders approved the 2016 Long-Term Incentive Plan (the "2016 Plan"). The Company reserved 2,000,000 shares of common stock for the Company to grant stock options, restricted stock, cash-settled stock appreciation rights ("SARs") and other stock-based awards to certain officers, directors and employees of the Company under the 2016 Plan. The 2016 Plan is administered by the Company’s compensation committee of the Board of Directors. As of December 31, 2017, a portion of unvested restricted stock, and unexercised stock options and cash-settled SARs remain outstanding under the 2006 Long-Term Incentive Plan which has otherwise expired. Employee Stock Purchase Plan In 2014, the Company adopted the 2014 Employee Stock Purchase Plan ("ESPP") and reserved 1,000,000 shares of common stock for employee purchases under the plan. Shares are purchased semi-annually, at a 10 percent discount, based on the market value at period-end. Employees may contribute up to 25 percent of their base pay per offering period, not to exceed $25,000 each calendar year, for the purchase of common stock. The ESPP is a compensatory plan under applicable accounting guidance and results in the recognition of compensation expense. During 2017 , 2016 and 2015 , employees purchased 18,498 , 13,400 and 8,306 shares under the ESPP, respectively. Compensation expense For the years ended December 31, 2017 , 2016 and 2015 , the Company recorded compensation expense of $14.0 million , $9.6 million and $10.6 million respectively, related to stock options, restricted stock, cash-settled SARs and the ESPP. Forfeiture rates are estimated at the time of grant based on historical actuals for similar grants, and are matched to actuals over the vesting period. The unrecognized compensation cost and weighted-average period over which the cost is expected to be recognized for non-vested awards as of December 31, 2017 , are presented below: Unrecognized Compensation Cost (thousands) Weighted Average Period (years) Restricted stock $ 19,730 1.74 Cash-settled SARs 481 1.62 Stock options — — Total $ 20,211 1.73 Stock options The fair value of stock options granted is estimated as of the grant date using the Black-Scholes option pricing model. The contractual terms of the Company’s stock option awards granted range from five to ten years. A summary of option activity as of December 31, 2017 , 2016 and 2015 , and changes during the years then ended, is presented below: Options Weighted Average Exercise Price Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value (thousands) Outstanding at December 31, 2014 88,749 $ 69.43 3.29 $ 7,180 Exercised (36,968 ) $ 52.06 Forfeited (3,000 ) $ 3.50 Outstanding at December 31, 2015 48,781 $ 86.65 2.62 $ 3,960 Exercised (5,192 ) 108.59 Outstanding at December 31, 2016 43,589 $ 84.04 1.55 $ 3,590 Exercised (16,014 ) $ 60.20 Outstanding at December 31, 2017 27,575 $ 97.88 0.72 $ 1,568 Fully vested and expected to vest at December 31, 2017 27,575 $ 97.88 0.72 $ 1,568 Exercisable at December 31, 2017 27,575 $ 97.88 0.72 $ 1,568 During the years ended December 31, 2017 , 2016 and 2015 , the total intrinsic value of options exercised was $1.3 million , $0.2 million and $5.8 million , respectively. Cash received from option exercises for the years ended December 31, 2017 , 2016 and 2015 was $1.0 million , $0.6 million and $1.9 million , respectively. Restricted stock awards The closing price of the Company's stock on the date of grant is used as the fair value for the issuance of restricted stock. A summary of the status of the Company’s non-vested restricted stock grants during the years ended December 31, 2017 , 2016 and 2015 is presented below: Shares Weighted Average Grant Date Fair Value Non-vested at December 31, 2014 98,782 $ 91.15 Granted 47,810 178.68 Vested (54,825 ) 83.35 Forfeited (8,810 ) 130.35 Non-vested at December 31, 2015 82,957 $ 155.30 Granted 224,018 144.74 Vested (43,310 ) 129.96 Forfeited (10,007 ) 158.74 Non-vested at December 31, 2016 253,658 $ 146.01 Granted 125,442 165.61 Vested (91,338 ) 145.08 Forfeited (94,872 ) 157.95 Non-vested at December 31, 2017 192,890 $ 153.32 The total fair value of restricted stock that vested during the years ended December 31, 2017 , 2016 and 2015 was $13.3 million , $5.6 million and $4.6 million , respectively. Cash-settled SARs Cash-settled SARs are liability classified awards for which the fair value and compensation expense recognized are updated monthly, also using the Black-Scholes option pricing model. The following range of assumptions in the Black-Scholes pricing model was used to determine fair value as of December 31 of the years indicated below: 2017 2016 2015 Weighted-average volatility 32.8 % 33.2 % 30.2 % Expected term (in years) 0.2 - 1.9 0.3 - 3.1 0.3 - 2.5 Risk-free interest rate 0.6% - 1.9% 0.4% - 1.5% 0.3% - 1.2% Dividend yield 1.62 % 1.51 % 1.47 % Expected volatilities used for award valuation are based on the historical volatility of the Company's common stock price. Expected term represents the weighted average time between the award’s grant date and its expected exercise date. The Company estimated the expected term assumption in 2017 , 2016 and 2015 using historical award exercise activity and employee termination activity. The risk-free interest rate for periods equal to the expected term of an award is based on a blended historical rate using Federal Reserve rates for U.S. Treasury securities. The dividend yield reflects the effect that paying a dividend has on the fair value of the Company's stock. The contractual terms of the Company’s cash-settled SARs awards granted are five years. A summary of cash-settled SARs awards activity during the years ended December 31, 2017 , 2016 and 2015 is presented below: # of SARs Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value (thousands) Balance at December 31, 2014 119,513 $ 86.23 Granted 77,396 181.47 Forfeited (21,722 ) 135.16 Exercised (43,446 ) 80.10 Balance at December 31, 2015 131,741 136.13 Granted 15,000 146.03 Forfeited (10,083 ) 170.21 Exercised (32,050 ) 89.19 Balance at December 31, 2016 104,608 153.86 Forfeited (14,682 ) 177.6 Exercised (9,462 ) 106.25 Balance at December 31, 2017 80,464 $ 155.13 2.13 $ — Vested or expected to vest at December 31, 2017 74,122 $ 155.02 2.14 $ — Exercisable at December 31, 2017 57,433 $ 150.74 1.85 $ 230

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Future minimum fixed payments for commitments as of December 31, 2017 (in thousands): 2018 2019 2020 2021 2022 2023 -Thereafter Operating lease obligations $ 7,455 $ 6,592 $ 4,716 $ 2,768 $ 1,071 $ 5,824 Aircraft acquisition obligations (1) 150,264 97,310 66,560 32,375 29,155 198,450 Airport fees under use and lease agreements 11,336 10,454 5,224 63 — — Total future payments $ 169,055 $ 114,356 $ 76,500 $ 35,206 $ 30,226 $ 204,274 (1) Includes purchase obligations and capital lease obligations. Operating Lease Obligations The Company leases assets including office facilities, office equipment, certain airport and terminal facilities, and other space leases. These commitments have remaining non-cancelable lease terms, which range from 2019 to 2036. Total rental expense for operating leases for the years ended December 31, 2017 , 2016 and 2015 was $9.0 million , $8.1 million and $7.9 million , respectively. Aircraft sub-service expense was $3.1 million , $0.9 million , and $2.1 million , in 2017, 2016 and 2015, respectively. Aircraft Commitments During 2017, the Company entered into three purchase agreements for six Airbus A320 series aircraft. Four of these aircraft were acquired in 2017 and the remaining two were acquired after the end of the year. During 2017, the Company also entered into 13 capital lease agreements, each for one Airbus A320 series aircraft, which are scheduled to be delivered in 2018. During 2016, the Company entered into four purchase agreements for 27 Airbus A320 series aircraft yet to be purchased by the end of 2016, including an agreement for 12 newly manufactured Airbus A320 aircraft. Of these aircraft, 13 were acquired in 2017, seven are scheduled to be acquired in 2018, and the remaining seven are expected to be acquired in 2019 and 2020. During 2015, the Company entered into one purchase agreement for four Airbus A320 series aircraft yet to be purchased by the end of 2015 or 2016. These aircraft were acquired in 2017. Airport and Other Facility Lease Obligations The Company leases other facilities in Las Vegas, Florida and throughout our network with approximately 500,000 square feet of space used for other corporate purposes. These leases expire between 2019 and 2036. The Company is responsible for its share of common area maintenance charges under each lease. Airport and terminal facility leases are entered into with a number of local governments and other third parties. These lease arrangements have a variety of terms and conditions. Contingencies The Company is subject to certain legal and administrative actions it considers routine to its business activities. The Company believes the ultimate outcome of any pending legal or administrative matters will not have a material adverse impact on its financial position, liquidity or results of operations.

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts (Notes)	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	Valuation and Qualifying Accounts (in thousands) Balance at Beginning of Year Changes Charged to Statement of Income Account Balance at End of Year Allowance for expendable parts and supplies For the Year Ended December 31, 2017 (1) $ 7,205 $ 6,551 $ 13,756 For the Year Ended December 31, 2016 4,607 2,598 7,205 For the Year Ended December 31, 2015 3,003 1,604 4,607 (1) Changes during the year and ending balance include additional reserve of $2.0 million related to the MD-80 impairment charge.

Subsequent Events (Notes)

Subsequent Events (Notes)	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events In January 2018, the Company executed a purchase agreement for one Airbus A320 series aircraft, for which delivery is expected in the second quarter 2019.

Summary of Significant Accoun23

Summary of Significant Accounting Policies - (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation [Policy Text Block]	Basis of Presentation The accompanying consolidated financial statements include the accounts of Allegiant Travel Company (the "Company") and its wholly-owned operating subsidiaries. The Company has no independent assets or operations, and all guarantees of the Company's publicly held debt are full and unconditional and joint and several. Any subsidiaries of the parent company other than the subsidiary guarantors are minor. The Company's investments in unconsolidated affiliates, which are 50 percent or less owned, are accounted for under the equity and cost method. All intercompany balances and transactions have been eliminated. Certain reclassifications have been made to the prior period amounts to conform to current year presentation.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities, at the date of the financial statements based on events and transactions occurring during the periods reported, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents Cash and cash equivalents include investments and interest bearing instruments with maturities of three months or less at the balance sheet date. Such investments are carried at cost which approximates fair value.
Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]	Restricted Cash Restricted cash represents escrowed funds under fixed fee contracts, and cash collateral against letters of credit required by hotel properties for guaranteed room availability, airports and certain other parties. Restricted cash at December 31, 2017 and 2016 was $11.2 million and $11.6 million , respectively.
Receivables, Policy [Policy Text Block]	Accounts Receivable Accounts receivable are carried at face amount which approximates fair value. They consist primarily of amounts due from credit card companies associated with the sale of tickets for future travel, commission amounts due from Enterprise Holdings Inc., based on terms in the rental car provider agreement, income tax receivables, and amounts due related to fixed fee charter agreements. If deemed necessary, the Company records charges to its allowance for doubtful accounts for amounts not expected to be collected. The allowance for doubtful accounts was zero as of December 31, 2017 and 2016 . The Company also had an outstanding receivable from a third party as of December 31, 2017 , for which $6.3 million is due more than one year after the balance sheet date and is classified with the Company's other assets.
Marketable Securities, Policy [Policy Text Block]	Short-term and Long-term Investments The Company’s investments in marketable securities are classified as available-for-sale and are reported at fair value with the net unrealized gain or (loss) reported as a component of accumulated other comprehensive income in shareholders’ equity. Investment securities are classified as cash equivalents, short-term investments and long-term investments based on maturity date as of the balance sheet date. Cash equivalents have maturities of three months or less, short-term investments have maturities of greater than three months but equal to or less than one year, and long-term investments are those with a maturity date greater than one year. As of December 31, 2017 , the Company’s long-term investments consisted of corporate debt securities, federal agency debt securities, US Treasury Bonds, and municipal debt securities with contractual maturities of less than 24 months. The amortized cost of investment securities sold is determined by the specific identification method with any realized gains or losses reflected in other (income) expense. The Company had minimal realized losses during the years ended December 31, 2017 , 2016 , and 2015 . The Company believes unrealized losses related to debt securities are not other-than-temporary and does not intend to sell these securities prior to amortized cost recoverability. The Company attempts to minimize its concentration risk with regard to its cash, cash equivalents, and investment portfolio. This is accomplished by diversifying and limiting amounts among different counterparties, the type of investment, and the amount invested in any individual security, commercial paper, or money market fund.
Inventory, Policy [Policy Text Block]	Expendable Parts, Supplies and Fuel, Net Expendable parts, supplies and fuel inventories are valued at cost using the first-in, first-out method. Such inventories are charged to expense as they are used in operations. An obsolescence allowance for expendable parts and supplies is based on the remaining useful lives of the corresponding fleet type and salvage values. The allowance for expendable parts and supplies was $13.8 million and $7.2 million at December 31, 2017 and 2016 , respectively. Rotable aircraft parts inventories are included in property and equipment.
Internal Use Software, Policy [Policy Text Block]	Software Capitalization The Company capitalizes certain internal and external costs related to the acquisition and development of computer software during the application development stage of projects. The Company amortizes these capitalized costs using the straight-line method over the estimated useful life of the software, which typically ranges from three to five years. The Company had unamortized computer software development costs of $41.0 million and $40.4 million as of December 31, 2017 and 2016 , respectively. Amortization expense related to computer software was $15.9 million , $13.3 million and $10.0 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. Costs incurred during the preliminary and post-implementation stages are expensed as incurred.
Property, Plant and Equipment, Policy [Policy Text Block]	Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over their estimated useful lives less an estimated salvage value. The estimated useful lives of the principal asset classes are shown below. As of December 31, 2017 , our MD-80 fleet has been fully impaired and has no remaining depreciable book value. Aircraft, engines and related rotable parts 10-25 years Buildings 25 years Equipment and leasehold improvements 3-7 years Computer hardware and software 3-5 years In estimating the useful lives and residual values of aircraft, the Company primarily has relied upon actual experience with the same or similar aircraft types, current and projected future market information, and recommendations from other industry sources. Subsequent revisions to these estimates could be caused by changing market prices of the Company’s aircraft, changes in utilization of the aircraft, and other fleet events. These estimates are evaluated each reporting period and adjusted if necessary. Changes in the estimate for useful lives or residual values of the Company’s property and equipment could result in an acceleration of depreciation expense associated with the change in estimate. Payments required to be made in advance of aircraft delivery are qualifying assets and interest attributable to these payments is capitalized as part of the cost of the related asset until the aircraft has been delivered and is ready to enter revenue service. Interest is capitalized at the Company’s weighted average borrowing rate and depreciated over the estimated useful life of the asset. Capitalized interest for 2017 was $3.2 million and $1.8 million in 2016.
Measurement of Impairment of Long-Lived Assets, Policy [Policy Text Block]	Measurement of Impairment of Long-Lived Assets The Company records impairment losses on long-lived assets used in operations, consisting principally of property and equipment, when events or changes in circumstances indicate, in management’s judgment, that the assets might be impaired, and the undiscounted future cash flows estimated to be generated by those assets are less than the carrying amount of those assets. In making these determinations, the Company utilizes certain assumptions, including, but not limited to: (i) estimated fair value of the assets; and (ii) estimated future cash flows expected to be generated by these assets, which are based on additional assumptions such as asset utilization, length of service for which the asset will be used in operations, and estimated salvage values. For the year ended December 31, 2017 , the Company recorded a non-cash impairment charge of $35.3 million on its fleet of MD-80 aircraft, engines, and related assets, as a result of its review of fleet value. This represents a full impairment of these assets, and as such, these assets have no remaining book value. The Company analyzed many factors, including the accelerated retirement dates of the MD-80 fleet, a reduction in aircraft utilization due to the continued induction of Airbus A320 series aircraft, and the significantly decreased level of demand in the secondary market for MD-80 aircraft, spare engines, and parts. For the years ended December 31, 2017, 2016 and 2015 , the Company incurred impairment losses related to various aircraft parts, of $1.3 million , $3.0 million , and $1.1 million , respectively and classified within Other operating expense.
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition Scheduled service revenue Scheduled service revenue consists of passenger revenue generated from nonstop flights in the Company’s route network, recognized either when the travel-related service or transportation is provided or when the itinerary expires unused. Nonrefundable scheduled itineraries expire on the date of the intended flight, unless the date is extended by notification from the customer in advance. Itineraries sold for transportation not yet used, as well as unexpired credits, are included in air traffic liability. Various taxes and fees, assessed on the sale of tickets to customers, are collected by the Company serving as an agent, and remitted to taxing authorities. These taxes and fees are not included as revenue in the Company’s consolidated statements of income and are recorded as a liability until remitted to the appropriate taxing authority. Ancillary air-related revenue Ancillary air-related revenue is generated from fees paid by ticketed passengers and consists of baggage fees, the use of the Company’s website to purchase scheduled service transportation, advance seat assignments, and other services. Revenues from air-related charges are recognized when the transportation is provided if the product is not deemed distinct of the original ticket sale. Change and cancellation fees for nonrefundable itineraries are air-related charges deemed distinct of the original ticket sale, and are recognized as revenue when the fee is incurred by the customer. Ancillary third party revenue Ancillary revenue is also generated from the sale of third party products such as hotel rooms, rental cars and ticket attractions. Revenue from the sale of third party products is recognized at the time the product is utilized, such as the time a purchased hotel room is occupied. The Company follows accounting standards for determining whether it is a principal or an agent in revenue arrangements to determine the amount of revenue to be recognized for each element of a bundled sale involving air-related charges and third party products in addition to airfare. Revenue from the sale of third party products is recorded net (treatment as an agent) of amounts paid to wholesale providers, travel agent commissions, and transaction costs. Fixed fee contract revenue Fixed fee contract revenue consists of agreements to provide charter service on a year-round and ad hoc basis. Fixed fee contract revenue is recognized when the transportation is provided. Other revenue Other revenue is generated from leased aircraft, engines, and other miscellaneous sources. Lease revenue is recognized ratably over the lease term. Affinity Credit Card Program The Allegiant World Mastercard® is issued by Bank of America through which arrangement points are sold and consideration is received under an agreement with a seven year scheduled duration expiring in 2023. Under this arrangement, the Company identified the following deliverables: travel points to be awarded (the travel component), use of the Company’s brand and access to its member lists, and certain other advertising and marketing elements (collectively the marketing component). Applying guidance under Accounting Standards Update (“ASU”) 2009-13 - Revenue Recognition (Topic 605): Multiple-Deliverable Revenue Arrangements, each of these deliverables is accounted for separately and allocation of the consideration from the agreement is determined based on the relative selling price of each deliverable. The Company applied a level of management judgment and estimation in determining the best estimate of selling price for each deliverable by considering multiple inputs and methods including, but not limited to, the redemption value of points awarded, discounted cash flows, brand value, volume discounts, published selling prices, number of points to be awarded and number of points to be redeemed. The travel component is deferred based on its relative selling price and is recognized into scheduled service revenue when the points are redeemed by cardholders. The marketing component is considered earned in the period in which points are sold and is therefore recognized into third party products revenue in the same period.
Maintenance and Repair Costs, Policy [Policy Text Block]	Aircraft Maintenance and Repair Costs The Company accounts for non-major maintenance and repair costs incurred under the direct expense method. Under this method, maintenance and repair costs for owned and leased aircraft are charged to operating expenses as incurred. Maintenance and repair costs includes all parts, materials, line maintenance, and non-major maintenance activities required to maintain the Company's multiple fleet types. The Company accounts for major maintenance costs of its MD-80 airframes and the related JT8D-219 engines using the direct expense method. Under this method, major maintenance costs are charged to expense as incurred. The Company accounts for major maintenance costs of its Airbus airframes and the related CFM engines using the deferral method. Under this method, the Company capitalizes the cost of major maintenance events, which are amortized as a component of depreciation and amortization expense, over the estimated period until the next scheduled major maintenance event. During 2017 and 2016, the Company deferred $20.7 million and $18.9 million of costs for major maintenance with associated amortization expense charged to depreciation and amortization of $6.7 million and $1.5 million , respectively.
Advertising Costs, Policy [Policy Text Block]	Advertising Costs Advertising costs are charged to expense in the period incurred. Advertising expense was $20.9 million , $13.6 million and $12.7 million for the years ended December 31, 2017 , 2016 and 2015 , respectively.
Earnings Per Share, Policy [Policy Text Block]	Earnings per Share Basic and diluted earnings per share are computed pursuant to the two-class method as opposed to the treasury method. Under this method, the Company attributes net income to two classes, common stock and unvested restricted stock awards. Unvested restricted stock awards granted to employees under the Company’s Long-Term Incentive Plan are considered participating securities because they receive non-forfeitable rights to cash dividends at the same rate as common stock. Diluted net income per share is calculated using the more dilutive of two methods. Under both methods, the exercise of employee stock options is assumed using the treasury stock method. The assumption of vesting of restricted stock, however, differs as described below: 1. Assume vesting of restricted stock using the treasury stock method. 2. Assume unvested restricted stock awards are not vested, and allocate earnings to common shares and unvested restricted stock awards using the two-class method. For the years ended December 31, 2017 , 2016 and 2015 , the second method above was used in the computation because it was more dilutive than the first method. The following table sets forth the computation of net income per share on a basic and diluted basis for the periods indicated (in thousands, except per share amounts): Year ended December 31, 2017 2016 2015 Basic: Net income $ 194,902 $ 219,590 $ 220,374 Less net income allocated to participating securities (2,917 ) (1,748 ) (961 ) Net income attributable to common stock $ 191,985 $ 217,842 $ 219,413 Net income per share, basic $ 11.94 $ 13.23 $ 12.97 Weighted-average shares outstanding 16,073 16,465 16,923 Diluted: Net income $ 194,902 $ 219,590 $ 220,374 Less net income allocated to participating securities (2,914 ) (1,746 ) (958 ) Net income attributable to common stock $ 191,988 $ 217,844 $ 219,416 Net income per share, diluted $ 11.93 $ 13.21 $ 12.94 Weighted-average shares outstanding 16,073 16,465 16,923 Dilutive effect of stock options and restricted stock 74 42 69 Adjusted weighted-average shares outstanding under treasury stock method 16,147 16,507 16,992 Participating securities excluded under two-class method (52 ) (18 ) (30 ) Adjusted weighted-average shares outstanding under two-class method 16,095 16,489 16,962 Stock awards outstanding of 5,752 ; 1,918 ; and 28,789 shares for 2017 , 2016 , and 2015 , respectively, were excluded from the computation of diluted earnings per share as they were antidilutive.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	Share-Based Compensation The Company accounts for share-based compensation in accordance with accounting standards which require the compensation cost related to share-based payment transactions be recognized in the Company’s consolidated statements of income. The cost is measured at the grant date, based on the calculated fair value of the award using the Black-Scholes option pricing model for cash-settled SARs, and is remeasured monthly for cash-settled SARs. Fair value is based on the closing price of the Company’s stock on the grant date for restricted stock awards. The cost is recognized as an expense over the requisite service period (the vesting period of the award) which is generally three years. Forfeiture rates for each type of award are estimated at time of grant. The Company’s share-based employee compensation plan is more fully discussed in Note 11- Employee Benefit Plans.
Income Tax, Policy [Policy Text Block]	Income Taxes The Company recognizes deferred income taxes based on the asset and liability method required by accounting standards. Deferred tax assets and liabilities are determined based on the timing differences between book basis for financial reporting purposes and tax basis of the asset and liability and measured using the enacted tax rates. A valuation allowance for deferred tax assets is provided if it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company determines the net non-current deferred tax assets or liabilities separately for federal, state, foreign and other local jurisdictions. The Company’s income tax returns are subject to examination by the Internal Revenue Service (“IRS”) and other tax authorities in the jurisdictions where the Company operates. The Company assesses potentially unfavorable outcomes of such examinations based on the criteria set forth in uncertain tax position accounting standards. The accounting standards prescribe a minimum recognition threshold a tax position is required to meet before being recognized in the financial statements. Accounting standards for income taxes utilize a two-step approach for evaluating tax positions. Recognition (Step I) occurs when the Company concludes that a tax position, based on its technical merits, is more likely than not to be sustained upon examination. Measurement (Step II) is only addressed if the position is deemed to be more likely than not to be sustained. Under Step II, the tax benefit is measured as the largest amount of benefit that is greater than 50 percent likely of being realized upon settlement. The tax positions failing to qualify for initial recognition are recognized in the first subsequent interim period they meet the “more likely than not” standard. If it is subsequently determined that a previously recognized tax position no longer meets the “more likely than not” standard, it is required that the tax position be derecognized. As applicable, the Company will recognize accrued penalties and interest related to unrecognized tax benefits in the provision for income taxes.
New Accounting Pronouncements, Policy [Policy Text Block]	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board ("FASB") issued ASU 2014-09, "Revenue from Contracts with Customers (Topic 606)" intended to create a unified model to determine when and how revenue is recognized. Under this ASU and subsequently issued amendments, the core principle is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration for which the entity expects to be entitled in exchange for those goods or services. The Company will adopt this standard using the full-retrospective approach on January 1, 2018. Under the new standard, revenue for certain air-related ancillary fees that are directly related to ticket revenue, such as seat fees and baggage fees, will no longer be considered distinct performance obligations separate from passenger travel and will be reclassified into scheduled service revenue. The amounts expected to be reclassified from air-related charges into scheduled service revenue will be between approximately $536 million and $546 million for 2017 and between $490 million and $500 million for 2016. In addition, certain fees previously recognized when incurred by the customer, will be deferred and recognized as revenue when air travel is provided and reclassified into scheduled service revenue, as well as reclassification of certain expense items to scheduled service revenue. Although the Company is in the process of finalizing analysis needed to recast prior periods, it is believed that adoption will not have a material effect on earnings. In January 2016, the FASB issued ASU 2016-01, a standard which includes several changes to financial instruments, including the elimination of the available-for-sale classification of equity investments, requiring those with readily determinable fair values to be measured at fair value with changes in fair value recognized in net income. The standard is effective for annual and interim periods beginning after December 15, 2017, and the Company will adopt it effective January 1, 2018. The Company does not expect the adoption will have a material impact on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02 related to leases. This standard will require leases with durations greater than twelve months to be recognized on the balance sheet as a lease liability and a corresponding right-of-use asset, and is effective for interim and annual reporting periods beginning after December 15, 2018 with early adoption permitted. The Company has not completed the assessment of this new standard. The Company believes adoption will have a significant impact on its consolidated balance sheets but is not expected to significantly change the recognition or measurement of associated expense within the consolidated statements of income or cash flows. In August 2016, the FASB issued ASU 2016-15, which amends the guidance in Accounting Standards Codification ("ASC") 230 on the classification of certain cash receipts and payments in the statement of cash flows. The primary purpose of the ASU is to reduce the diversity in practice that has resulted from the lack of consistency on this topic. The standard is effective for annual and interim periods beginning after December 15, 2017, and the Company will adopt it effective January 1, 2018. Significant classification modifications are not expected as a result of adoption. In November 2016, the FASB issued ASU 2016-18 which clarifies the presentation of restricted cash and restricted cash equivalents on the statement of cash flows. This ASU requires that the change in total cash, cash at beginning of period and cash at end of period on the statement of cash flows include restricted cash and restricted cash equivalents and also requires companies reporting cash and restricted cash separately on the balance sheet to reconcile those amounts to the statement of cash flows. The standard is to be applied retrospectively and is effective for annual and interim periods beginning after December 15, 2017. The Company will adopt it effective January 1, 2018 and does not expect the adoption will have a material impact on its consolidated financial statements.

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Unrealized Gain (Loss) on Investments
Estimated Useful Lives	As of December 31, 2017 , our MD-80 fleet has been fully impaired and has no remaining depreciable book value. Aircraft, engines and related rotable parts 10-25 years Buildings 25 years Equipment and leasehold improvements 3-7 years Computer hardware and software 3-5 years Property and equipment consisted of the following (in thousands): As of December 31, 2017 As of December 31, 2016 Flight equipment, including pre-delivery deposits $ 1,539,433 $ 1,377,829 Computer hardware and software 123,675 101,850 Other property and equipment 125,855 81,786 Total property and equipment 1,788,963 1,561,465 Less accumulated depreciation and amortization (276,548 ) (466,151 ) Property and equipment, net $ 1,512,415 $ 1,095,314
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the computation of net income per share on a basic and diluted basis for the periods indicated (in thousands, except per share amounts): Year ended December 31, 2017 2016 2015 Basic: Net income $ 194,902 $ 219,590 $ 220,374 Less net income allocated to participating securities (2,917 ) (1,748 ) (961 ) Net income attributable to common stock $ 191,985 $ 217,842 $ 219,413 Net income per share, basic $ 11.94 $ 13.23 $ 12.97 Weighted-average shares outstanding 16,073 16,465 16,923 Diluted: Net income $ 194,902 $ 219,590 $ 220,374 Less net income allocated to participating securities (2,914 ) (1,746 ) (958 ) Net income attributable to common stock $ 191,988 $ 217,844 $ 219,416 Net income per share, diluted $ 11.93 $ 13.21 $ 12.94 Weighted-average shares outstanding 16,073 16,465 16,923 Dilutive effect of stock options and restricted stock 74 42 69 Adjusted weighted-average shares outstanding under treasury stock method 16,147 16,507 16,992 Participating securities excluded under two-class method (52 ) (18 ) (30 ) Adjusted weighted-average shares outstanding under two-class method 16,095 16,489 16,962

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Schedule Of Property Plant And Equipment	As of December 31, 2017 , our MD-80 fleet has been fully impaired and has no remaining depreciable book value. Aircraft, engines and related rotable parts 10-25 years Buildings 25 years Equipment and leasehold improvements 3-7 years Computer hardware and software 3-5 years Property and equipment consisted of the following (in thousands): As of December 31, 2017 As of December 31, 2016 Flight equipment, including pre-delivery deposits $ 1,539,433 $ 1,377,829 Computer hardware and software 123,675 101,850 Other property and equipment 125,855 81,786 Total property and equipment 1,788,963 1,561,465 Less accumulated depreciation and amortization (276,548 ) (466,151 ) Property and equipment, net $ 1,512,415 $ 1,095,314

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): As of December 31, 2017 As of December 31, 2016 Salaries, wages and benefits $ 35,516 $ 38,860 Interest 13,326 11,891 Station expenses 12,026 14,799 Passenger fees 11,420 11,200 Property taxes 7,851 6,613 Maintenance and repairs 5,481 4,953 Advertising accruals 4,154 676 Passenger taxes 447 394 Other accruals 14,906 7,275 Total accrued liabilities $ 105,127 $ 96,661

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Summary of Long-Term Debt	Long-term debt consisted of the following (in thousands): As of December 31, 2017 As of December 31, 2016 Fixed-rate notes payable due through 2020 $ 465,462 $ 465,748 Variable-rate notes payable due through 2027 699,430 342,526 Total long-term debt, net of related costs 1,164,892 808,274 Less current maturities, net of related costs 214,761 86,226 Long-term debt, net of current maturities and related costs $ 950,131 $ 722,048 Weighted average fixed-interest rate 5.4 % 5.4 % Weighted average variable-interest rate 3.3 % 3.2 %

Stockholders' Equity Share Repu

Stockholders' Equity Share Repurchases (Tables)	12 Months Ended
	Dec. 31, 2017
Share Repurchases [Abstract]
Treasury Stock [Text Block]	Share repurchases consisted of the following during the periods indicated: Twelve Months Ended December 31, 2017 2016 2015 Shares repurchased (1) 604,497 391,972 682,003 Average price per share $ 142.66 $ 164.99 $ 186.43 Total (in thousands) 86,240 64,673 127,147

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Assets Measured at Fair Value On a Recurring Basis	Financial instruments measured at fair value on a recurring basis (in thousands): As of As of Description Total Level 1 Level 2 Total Level 1 Level 2 Cash equivalents Commercial paper $ 27,910 $ — $ 27,910 $ — $ — $ — Municipal debt securities 2,782 — 2,782 1,843 — 1,843 Money market funds 1,297 1,297 — 123 123 — Federal agency debt securities — — — 19,399 — 19,399 Total cash equivalents 31,989 1,297 30,692 21,365 123 21,242 Short-term Commercial paper 108,678 — 108,678 108,372 — 108,372 Corporate debt securities 107,878 — 107,878 76,570 — 76,570 Municipal debt securities 101,290 — 101,290 78,826 — 78,826 Federal agency debt securities 31,428 — 31,428 3,895 — 3,895 US Treasury Bonds 3,407 — 3,407 1,606 — 1,606 Total short-term 352,681 — 352,681 269,269 — 269,269 Long-term Corporate debt securities 60,396 — 60,396 25,048 — 25,048 Municipal debt securities 9,405 — 9,405 72,623 — 72,623 Federal agency debt securities 5,775 — 5,775 24,160 — 24,160 US Treasury Bonds 2,994 — 2,994 3,003 — 3,003 Derivative instruments 282 — 282 1,660 — 1,660 Total long-term 78,852 — 78,852 126,494 — 126,494 Total financial instruments $ 463,522 $ 1,297 $ 462,225 $ 417,128 $ 123 $ 417,005
Debt Instrument, Fair Value Disclosure	Carrying value and estimated fair value of long-term debt, including current maturities (in thousands): As of December 31, 2017 As of December 31, 2016 Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Level Publicly held debt $ 451,321 $ 462,604 $ 452,179 $ 468,005 2 Non-publicly held debt 719,681 660,065 360,999 340,866 3 Total long-term debt $ 1,171,002 $ 1,122,669 $ 813,178 $ 808,871

Income Taxes Income Taxes (Tabl

Income Taxes Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	The components of income before taxes for domestic and foreign operations consisted of the following (in thousands): Twelve Months Ended December 31, 2017 2016 2015 Domestic $ 176,853 $ 329,818 $ 331,813 Foreign 18,693 16,140 14,906 Total $ 195,546 $ 345,958 $ 346,719
Schedule of Components of Income Tax Expense (Benefit)	The provision for income taxes is composed of the following (in thousands): Year Ended December 31, 2017 2016 2015 Current: Federal $ (44,385 ) $ 89,014 $ 108,119 State 664 5,204 6,501 Foreign 558 1,262 996 Total current (43,163 ) 95,480 115,616 Deferred: Federal 40,816 27,950 9,458 State 1,962 1,673 125 Foreign 1,029 1,265 1,190 Total deferred 43,807 30,888 10,773 Total income tax provision $ 644 $ 126,368 $ 126,389
Schedule of Effective Income Tax Rate Reconciliation	The effective tax rate on income before income taxes differed from the federal statutory income tax rate as follows (in thousands): Year Ended December 31, 2017 2016 2015 Income tax expense at federal statutory rate $ 68,441 $ 121,085 $ 121,352 State income taxes, net of federal income tax benefit 2,723 5,487 4,293 Federal tax reform impact (74,738 ) — — Other 4,218 (204 ) 744 Total income tax expense $ 644 $ 126,368 $ 126,389
Schedule of Deferred Tax Assets and Liabilities	The major components of the Company’s net deferred tax assets and liabilities are as follows (in thousands): As of December 31, 2017 2016 Deferred tax assets: Accrued vacation $ 690 $ 1,183 Accrued bonus 628 9,340 State taxes 318 2,187 Accrued property taxes 1,573 2,077 Other 3,679 1,910 Stock-based compensation expense 1,983 3,126 Net operating loss 635 — Less: valuation allowance 422 — Total deferred tax assets 9,084 19,823 Deferred tax liabilities: Prepaid expenses 4,275 5,049 Depreciation 118,743 86,981 Foreign deferred 4,569 3,131 Total deferred tax liabilities 127,587 95,161 Net deferred tax liabilities $ 118,503 $ 75,338

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Employee Benefit Plans [Abstract]
Schedule of Unrecognized Compensation Cost, Nonvested Awards [Table Text Block]	The unrecognized compensation cost and weighted-average period over which the cost is expected to be recognized for non-vested awards as of December 31, 2017 , are presented below: Unrecognized Compensation Cost (thousands) Weighted Average Period (years) Restricted stock $ 19,730 1.74 Cash-settled SARs 481 1.62 Stock options — — Total $ 20,211 1.73
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Table Text Block]	The following range of assumptions in the Black-Scholes pricing model was used to determine fair value as of December 31 of the years indicated below: 2017 2016 2015 Weighted-average volatility 32.8 % 33.2 % 30.2 % Expected term (in years) 0.2 - 1.9 0.3 - 3.1 0.3 - 2.5 Risk-free interest rate 0.6% - 1.9% 0.4% - 1.5% 0.3% - 1.2% Dividend yield 1.62 % 1.51 % 1.47 %
Schedule of Share-based Compensation, Stock Options, Activity	A summary of option activity as of December 31, 2017 , 2016 and 2015 , and changes during the years then ended, is presented below: Options Weighted Average Exercise Price Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value (thousands) Outstanding at December 31, 2014 88,749 $ 69.43 3.29 $ 7,180 Exercised (36,968 ) $ 52.06 Forfeited (3,000 ) $ 3.50 Outstanding at December 31, 2015 48,781 $ 86.65 2.62 $ 3,960 Exercised (5,192 ) 108.59 Outstanding at December 31, 2016 43,589 $ 84.04 1.55 $ 3,590 Exercised (16,014 ) $ 60.20 Outstanding at December 31, 2017 27,575 $ 97.88 0.72 $ 1,568 Fully vested and expected to vest at December 31, 2017 27,575 $ 97.88 0.72 $ 1,568 Exercisable at December 31, 2017 27,575 $ 97.88 0.72 $ 1,568
Schedule of Nonvested Restricted Stock Units Activity	A summary of the status of the Company’s non-vested restricted stock grants during the years ended December 31, 2017 , 2016 and 2015 is presented below: Shares Weighted Average Grant Date Fair Value Non-vested at December 31, 2014 98,782 $ 91.15 Granted 47,810 178.68 Vested (54,825 ) 83.35 Forfeited (8,810 ) 130.35 Non-vested at December 31, 2015 82,957 $ 155.30 Granted 224,018 144.74 Vested (43,310 ) 129.96 Forfeited (10,007 ) 158.74 Non-vested at December 31, 2016 253,658 $ 146.01 Granted 125,442 165.61 Vested (91,338 ) 145.08 Forfeited (94,872 ) 157.95 Non-vested at December 31, 2017 192,890 $ 153.32
Schedule Of Cash Settled Stock Appreciation Rights Activity	A summary of cash-settled SARs awards activity during the years ended December 31, 2017 , 2016 and 2015 is presented below: # of SARs Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value (thousands) Balance at December 31, 2014 119,513 $ 86.23 Granted 77,396 181.47 Forfeited (21,722 ) 135.16 Exercised (43,446 ) 80.10 Balance at December 31, 2015 131,741 136.13 Granted 15,000 146.03 Forfeited (10,083 ) 170.21 Exercised (32,050 ) 89.19 Balance at December 31, 2016 104,608 153.86 Forfeited (14,682 ) 177.6 Exercised (9,462 ) 106.25 Balance at December 31, 2017 80,464 $ 155.13 2.13 $ — Vested or expected to vest at December 31, 2017 74,122 $ 155.02 2.14 $ — Exercisable at December 31, 2017 57,433 $ 150.74 1.85 $ 230

Commitments and Contingencies S

Commitments and Contingencies Schedule of Future Minimum Payments (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule of Future Minimum Payments [Abstract]
Contractual Obligation, Fiscal Year Maturity Schedule [Table Text Block]	Future minimum fixed payments for commitments as of December 31, 2017 (in thousands): 2018 2019 2020 2021 2022 2023 -Thereafter Operating lease obligations $ 7,455 $ 6,592 $ 4,716 $ 2,768 $ 1,071 $ 5,824 Aircraft acquisition obligations (1) 150,264 97,310 66,560 32,375 29,155 198,450 Airport fees under use and lease agreements 11,336 10,454 5,224 63 — — Total future payments $ 169,055 $ 114,356 $ 76,500 $ 35,206 $ 30,226 $ 204,274

Valuation and Qualifying Acco33

Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts Disclosure [Line Items]
Schedule Of Valuation And Qualifying Accounts [Table Text Block]	Balance at Beginning of Year Changes Charged to Statement of Income Account Balance at End of Year Allowance for expendable parts and supplies For the Year Ended December 31, 2017 (1) $ 7,205 $ 6,551 $ 13,756 For the Year Ended December 31, 2016 4,607 2,598 7,205 For the Year Ended December 31, 2015 3,003 1,604 4,607 (1) Changes during the year and ending balance include additional reserve of $2.0 million related to the MD-80 impairment charge.

Summary of Significant Accoun34

Summary of Significant Accounting Policies - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Advertising Expense	$ 20,910	$ 13,591	$ 12,665
Asset Impairment Charges	35,253	0	0
Capitalized Computer Software, Net	41,037	40,392
Capitalized Computer Software, Amortization	$ 15,851	$ 13,281	$ 10,006
Significant Change in Unrecognized Tax Benefits, Nature of Event	50.00%

Summary of Significant Accoun35

Summary of Significant Accounting Policies Investment Securities (Details)	Dec. 31, 2017
Schedule of Available-for-sale Securities
Equity Method Investment, Ownership Percentage	50.00%

Summary of Significant Accoun36

Summary of Significant Accounting Policies Property, Plant and Equipment, Salvage Value, Percentage (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Interest Costs Capitalized	$ 3.2	$ 1.8
Building
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	P25Y
Equipment And Leasehold Improvements | Minimum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	P3Y
Equipment And Leasehold Improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	P7Y
Computer Hardware and Software | Minimum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	P3Y
Computer Hardware and Software | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	P5Y
Airbus A320 Aircraft Series | Aircraft And Engines | Minimum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	P10Y
Airbus A320 Aircraft Series | Aircraft And Engines | Maximum
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	P25Y

Summary of Significant Accoun37

Summary of Significant Accounting Policies Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 194,902	$ 219,590	$ 220,374
Less net income allocated to participating securities	(2,917)	(1,748)	(961)
Net income attributable to common stock	$ 191,985	$ 217,842	$ 219,413
Net income per share, basic	$ 11.94	$ 13.23	$ 12.97
Weighted-average shares outstanding	16,073,000	16,465,000	16,923,000
Net income attributable to common stock	$ 191,988	$ 217,844	$ 219,416
Less net income allocated to participating securities	$ (2,914)	$ (1,746)	$ (958)
Net income per share, diluted	$ 11.93	$ 13.21	$ 12.94
Dilutive effect of stock options and restricted stock	74,000	42,000	69,000
Adjusted weighted-average shares outstanding under treasury stock method	16,147,000	16,507,000	16,992,000
Participating securities excluded under two-class method	(52,000)	(18,000)	(30,000)
Adjusted weighted-average shares outstanding under two-class method	16,095,000	16,489,000	16,962,000

Summary of Significant Accoun38

Summary of Significant Accounting Policies Earnings Per Share Textual (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	5,752	1,918	28,789

Summary of Significant Accoun39

Summary of Significant Accounting Policies Measurement of Impairment of Long-Lived Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired Long-Lived Assets Held and Used [Line Items]
Restricted Cash and Cash Equivalents, Current	$ 11,190	$ 11,647
Asset Impairment Charges	35,253	0	$ 0
Spare engine parts
Impaired Long-Lived Assets Held and Used [Line Items]
Asset Impairment Charges	$ 1,300	$ 3,000	$ 1,107

Summary of Significant Accoun40

Summary of Significant Accounting Policies Recent Accounting Pronouncements (Details) - Accounting Standards Update 2014-09 [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Expected Increase (Decrease) in Passenger Revenue	$ 536	$ 490
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Expected Increase (Decrease) in Passenger Revenue	$ 546	$ 500

Summary of Significant Accoun41

Summary of Significant Accounting Policies Expendable Parts, Supplies and Fuel (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Expendable Parts, Supplies and Fuel [Abstract]
Inventory Valuation Reserves	$ 13,800	$ 7,200

Summary of Significant Accoun42

Summary of Significant Accounting Policies Accounts Receivable (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Allowance for Doubtful Accounts Receivable	$ 0	$ 0
Accounts Receivable, Gross, Noncurrent	$ 6.3

Summary of Significant Accoun43

Summary of Significant Accounting Policies Aircraft Maintenance and Repair Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Servicing Asset at Amortized Cost [Line Items]
Amortization of Other Deferred Charges	$ 6.7	$ 1.5
Deferred Costs for Heavy Maintenance	$ 20.7	$ 18.9

Property and Equipment (Details

Property and Equipment (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Aircraft	Jan. 31, 2018aircraft	Dec. 31, 2016USD ($)
Property, Plant and Equipment [Line Items]
Number Of Aircraft Committed To Purchase | Aircraft	16
Flight Equipment, Gross	$ 1,539,433		$ 1,377,829
Computer Hardware and Software	123,675		101,850
Property, Plant and Equipment, Other, Gross	125,855		81,786
Property, Plant and Equipment, Gross	1,788,963		1,561,465
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(276,548)		(466,151)
Property, Plant and Equipment, Net	1,512,415		$ 1,095,314
Land	$ 20,800
Airbus A320 Aircraft Series | Asset not in service
Property, Plant and Equipment [Line Items]
Number of Aircraft Owned | Aircraft	11
Subsequent Event
Property, Plant and Equipment [Line Items]
Number Of Aircraft Committed To Purchase | aircraft		1

Property and Equipment Total Ai

Property and Equipment Total Aircraft Fleet (Details)	12 Months Ended
	Dec. 31, 2017Aircraft
Asset not in service | Airbus A320 Aircraft Series
Property, Plant and Equipment [Line Items]
Number of Aircraft Owned	11

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accrued Liabilities, Current [Abstract]
Salaries, wages and benefits	$ 35,516	$ 38,860
Interest	13,326	11,891
Station expenses	12,026	14,799
Passenger fees	11,420	11,200
Property taxes		7,851	$ 6,613
Maintenance and repairs	5,481	4,953
Advertising accruals	4,154	676
Passenger taxes	447	394
Other accruals	14,906	7,275
Accrued liabilities	$ 105,127	$ 96,661

Accrued Liabilities Textual (De

Accrued Liabilities Textual (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2014
Other accruals	$ 14,906	$ 7,275
Dividends Payable, Amount Per Share	$ 2.80	$ 2.40	$ 1.10
Due July 2019
Unsecured Long-term Debt, Noncurrent		$ 150,000		$ 300,000
Debt Instrument, Interest Rate, Stated Percentage				5.50%
Information Technology [Member]
Other accruals	$ 4,964

Long-Term Debt (Detail)

Long-Term Debt (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Notes Payable	$ 1,171,002	$ 813,178
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	214,800
Long-term Debt, Maturities, Repayments of Principal in Year Two	561,600
Long-term Debt, Maturities, Repayments of Principal in Year Three	95,200
Long-term Debt, Maturities, Repayments of Principal in Year Four	68,000
Long-term Debt, Maturities, Repayments of Principal in Year Five	41,530
Long-term Debt, Maturities, Repayments of Principal after Year Five	183,752
Debt Issuance Costs, Gross	6,100	4,900
Total long-term debt, net of related costs	1,164,892	808,274
Long-term Debt, Current Maturities	214,761	86,226
Long-term Debt, Excluding Current Maturities	950,131	722,048
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	102,000
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 112,750	$ 0
Airbus A320 Aircraft Series
Variable Interest Entity, Qualitative or Quantitative Information, Purpose of VIE	3
Variable Rate
Long-term Debt, Weighted Average Interest Rate, at Point in Time	3.31%	3.16%
Fixed Rate
Long-term Debt, Weighted Average Interest Rate, at Point in Time	5.41%	5.41%
Fixed-rate notes payable due through 2020
Notes Payable	$ 465,462	$ 465,748
Variable Rate Notes Payable Through 2027
Notes Payable	$ 699,430	$ 342,526

Long-Term Debt - Components of

Long-Term Debt - Components of Long-Term Debt (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months		$ 214,800,000
Notes Payable		1,171,002,000	$ 813,178,000
Debt Instrument, Collateral	12
Secured Long-term Debt, Noncurrent		1,164,892,000	808,274,000
Line of Credit Facility, Remaining Borrowing Capacity		$ 41,300,000
Line of Credit Facility, Description				$ 56,000,000
Due July 2019
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.50%
Unsecured Long-term Debt, Noncurrent	$ 300,000,000		$ 150,000,000
Debt Instrument, Redemption Price, Percentage			101.50%
Airbus A320 Aircraft Series
Debt Instrument [Line Items]
Debt Instrument, Collateral		57	34
Variable Interest Entity, Qualitative or Quantitative Information, Purpose of VIE		3
Real Estate
Debt Instrument [Line Items]
Notes Payable		$ 15,700,000	$ 16,200,000

Stockholders' Equity (Detail)

Stockholders' Equity (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jan. 08, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Weighted Average Volatility Rate		32.80%	33.20%	30.20%
Stock Repurchased During Period, Shares		604,497	391,972
Shares Paid for Tax Withholding for Share Based Compensation		27,606	10,103	12,682
Stock Repurchased During Period, Shares (in Shares)				682,003
Treasury Stock Acquired, Average Cost Per Share (in Dollars per share)		$ 142.66	$ 164.99	$ 186,430
Stock Repurchased During Period, Value		$ 86,240	$ 64,673	$ 127,147
Stock Repurchase Program, Authorized Amount		100,000
Payments for Repurchase of Common Stock		$ 90,457	$ 66,371	$ 129,455
Dividends Payable, Amount Per Share		$ 2.80	$ 2.40	$ 1.10
Dividends		$ 45,720	$ 39,800	$ 18,700
Fair Value Assumptions, Expected Dividend Rate		1.62%	1.51%	1.47%
Special Dividend
Dividends Payable, Amount Per Share				$ 1.65
Dividends	$ 27,700

Fair Value Measurements (Detail

Fair Value Measurements (Detail) - Fair Value Measurements at Reporting Date Using - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Municipal debt securities | Fair Value, Inputs, Level 1 | Long-term investments
Investment Securities	$ 0	$ 0
Municipal debt securities | Fair Value, Inputs, Level 2 | Long-term investments
Investment Securities	9,405	72,623
Fair Value, Measurements, Recurring
Investment Securities	463,522	417,128
Fair Value, Measurements, Recurring | Short-term investments
Investment Securities	352,681	269,269
Fair Value, Measurements, Recurring | Long-term investments
Investment Securities	78,852	126,494
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Investment Securities	1,297	123
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Short-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Long-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Investment Securities	462,225	417,005
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Short-term investments
Investment Securities	352,681	269,269
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Long-term investments
Investment Securities	78,852	126,494
Fair Value, Measurements, Recurring | Commercial paper | Short-term investments
Investment Securities	108,678	108,372
Fair Value, Measurements, Recurring | Commercial paper | Fair Value, Inputs, Level 1 | Short-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | Commercial paper | Fair Value, Inputs, Level 2 | Short-term investments
Investment Securities	108,678	108,372
Fair Value, Measurements, Recurring | US Government Corporations and Agencies Securities | Short-term investments
Investment Securities	31,428	3,895
Fair Value, Measurements, Recurring | US Government Corporations and Agencies Securities | Long-term investments
Investment Securities	5,775	24,160
Fair Value, Measurements, Recurring | US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 1 | Short-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 1 | Long-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 2 | Short-term investments
Investment Securities	31,428	3,895
Fair Value, Measurements, Recurring | US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 2 | Long-term investments
Investment Securities	5,775	24,160
Fair Value, Measurements, Recurring | US Treasury Securities | Short-term investments
Investment Securities	3,407	1,606
Fair Value, Measurements, Recurring | US Treasury Securities | Long-term investments
Investment Securities	2,994	3,003
Fair Value, Measurements, Recurring | US Treasury Securities | Fair Value, Inputs, Level 1 | Short-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | US Treasury Securities | Fair Value, Inputs, Level 1 | Long-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | US Treasury Securities | Fair Value, Inputs, Level 2 | Short-term investments
Investment Securities	3,407	1,606
Fair Value, Measurements, Recurring | US Treasury Securities | Fair Value, Inputs, Level 2 | Long-term investments
Investment Securities	2,994	3,003
Fair Value, Measurements, Recurring | Municipal debt securities | Short-term investments
Investment Securities	101,290	78,826
Fair Value, Measurements, Recurring | Municipal debt securities | Long-term investments
Investment Securities	9,405	72,623
Fair Value, Measurements, Recurring | Municipal debt securities | Fair Value, Inputs, Level 1 | Short-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | Municipal debt securities | Fair Value, Inputs, Level 2 | Short-term investments
Investment Securities	101,290	78,826
Fair Value, Measurements, Recurring | Corporate debt securities | Short-term investments
Investment Securities	107,878	76,570
Fair Value, Measurements, Recurring | Corporate debt securities | Long-term investments
Investment Securities	60,396	25,048
Fair Value, Measurements, Recurring | Corporate debt securities | Fair Value, Inputs, Level 1 | Short-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | Corporate debt securities | Fair Value, Inputs, Level 1 | Long-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | Corporate debt securities | Fair Value, Inputs, Level 2 | Short-term investments
Investment Securities	107,878	76,570
Fair Value, Measurements, Recurring | Corporate debt securities | Fair Value, Inputs, Level 2 | Long-term investments
Investment Securities	60,396	25,048
Fair Value, Measurements, Recurring | Derivative Financial Instruments, Assets | Long-term investments
Investment Securities	282	1,660
Fair Value, Measurements, Recurring | Derivative Financial Instruments, Assets | Fair Value, Inputs, Level 1 | Long-term investments
Investment Securities	0	0
Fair Value, Measurements, Recurring | Derivative Financial Instruments, Assets | Fair Value, Inputs, Level 2 | Long-term investments
Investment Securities	282	1,660
Fair Value, Measurements, Recurring | Cash Equivalents
Cash Equivalents	31,989	21,365
Fair Value, Measurements, Recurring | Cash Equivalents | Fair Value, Inputs, Level 1
Cash Equivalents	1,297	123
Fair Value, Measurements, Recurring | Cash Equivalents | Fair Value, Inputs, Level 2
Cash Equivalents	30,692	21,242
Fair Value, Measurements, Recurring | Cash Equivalents | Money market funds
Cash Equivalents	1,297	123
Fair Value, Measurements, Recurring | Cash Equivalents | Money market funds | Fair Value, Inputs, Level 1
Cash Equivalents	1,297	123
Fair Value, Measurements, Recurring | Cash Equivalents | Money market funds | Fair Value, Inputs, Level 2
Cash Equivalents	0	0
Fair Value, Measurements, Recurring | Cash Equivalents | Commercial paper
Cash Equivalents	27,910	0
Fair Value, Measurements, Recurring | Cash Equivalents | Commercial paper | Fair Value, Inputs, Level 1
Cash Equivalents	0	0
Fair Value, Measurements, Recurring | Cash Equivalents | Commercial paper | Fair Value, Inputs, Level 2
Cash Equivalents	27,910	0
Fair Value, Measurements, Recurring | Cash Equivalents | US Government Corporations and Agencies Securities
Cash Equivalents	0	19,399
Fair Value, Measurements, Recurring | Cash Equivalents | US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 1
Cash Equivalents	0	0
Fair Value, Measurements, Recurring | Cash Equivalents | US Government Corporations and Agencies Securities | Fair Value, Inputs, Level 2
Cash Equivalents	0	19,399
Fair Value, Measurements, Recurring | Cash Equivalents | Municipal debt securities
Cash Equivalents	2,782	1,843
Fair Value, Measurements, Recurring | Cash Equivalents | Municipal debt securities | Fair Value, Inputs, Level 1
Cash Equivalents	0	0
Fair Value, Measurements, Recurring | Cash Equivalents | Municipal debt securities | Fair Value, Inputs, Level 2
Cash Equivalents	$ 2,782	$ 1,843

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Measurements Estimated Fair Value of Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Secured Long-term Debt, Noncurrent	$ 1,164,892	$ 808,274
Notes Payable	1,171,002	813,178
Special charge	35,253	0	$ 0
Publicly Held Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Secured Long-term Debt, Noncurrent	451,321	452,179
Non-Publicly Held Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Secured Long-term Debt, Noncurrent	719,681	360,999
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	1,122,669	808,871
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Publicly Held Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	462,604	468,005
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Non-Publicly Held Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	$ 660,065	$ 340,866

Derivative Instruments (Details

Derivative Instruments (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments Disclosure [Abstract]
Debt Instrument, Collateral	12
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		$ (871)	$ (424)	$ 874
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax		1,107	1,046	$ 1,292
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		3,000
Derivative, Notional Amount		$ 282	$ 1,700

Income Taxes Income Taxes (Deta

Income Taxes Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax Credit Carryforward [Line Items]
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	$ 68,441	$ 121,085	$ 121,352
Current Federal Tax Expense (Benefit)	(44,385)	89,014	108,119
Income taxes, net of refunds	(17,954)	110,612	111,399
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation			3,865
Current State and Local Tax Expense (Benefit)	664	5,204	6,501
Current Income Tax Expense (Benefit)	(43,163)	95,480	115,616
Deferred Federal Income Tax Expense (Benefit)	40,816	27,950	9,458
Deferred State and Local Income Tax Expense (Benefit)	1,962	1,673	125
DeferredTotalIncomeTaxExpenseBenefit	43,807	30,888	10,773
Income Tax Reconciliation, State and Local Income Taxes	2,723	5,487	4,293
Income Tax Reconciliation, Other Reconciling Items	$ 4,218	$ (204)	$ 744

Income Taxes The Major Componen

Income Taxes The Major Components of the Company's Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 422	$ 0
Deferred Tax Assets, Net of Valuation Allowance	9,084	19,823
Deferred Tax Liabilities, Net, Noncurrent	(118,492)	(75,338)
Accrued Vacation
Valuation Allowance
Deferred Tax Assets, Gross	690	1,183
Deferred Tax Assets, Accrued Bonus
Valuation Allowance
Deferred Tax Assets, Gross	628	9,340
State Taxes
Valuation Allowance
Deferred Tax Assets, Gross	318	2,187
Accrued Property Taxes
Valuation Allowance
Deferred Tax Assets, Gross	1,573	2,077
Other 1
Valuation Allowance
Deferred Tax Assets, Gross	3,679	1,910
Stock Based Compensation
Valuation Allowance
Deferred Tax Assets, Gross	1,983	3,126
Valuation Allowance, Operating Loss Carryforwards
Valuation Allowance
Deferred Tax Assets, Gross	635	0
Prepaid Expenses
Valuation Allowance
Deferred Tax Liabilities, Gross, Noncurrent	4,275	5,049
Depreciation
Valuation Allowance
Deferred Tax Liabilities, Gross, Noncurrent	118,743	86,981
Foreign deferred
Valuation Allowance
Deferred Tax Liabilities, Gross, Noncurrent	4,569	3,131
Total Noncurrent
Valuation Allowance
Deferred Tax Liabilities, Net	127,587	95,161
Total
Valuation Allowance
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	$ (118,503)	$ (75,338)

Income Taxes The Components of

Income Taxes The Components of the Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
The Components of the Provision (Benefit) for Income Taxes [Abstract]
Current Federal Tax Expense (Benefit)	$ (44,385)	$ 89,014	$ 108,119
Current State and Local Tax Expense (Benefit)	664	5,204	6,501
Current Foreign Tax Expense (Benefit)	558	1,262	996
Current Income Tax Expense (Benefit)	(43,163)	95,480	115,616
Deferred Federal Income Tax Expense (Benefit)	40,816	27,950	9,458
Deferred State and Local Income Tax Expense (Benefit)	1,962	1,673	125
Deferred Foreign Income Tax Expense (Benefit)	1,029	1,265	1,190
DeferredTotalIncomeTaxExpenseBenefit	43,807	30,888	10,773
PROVISION FOR INCOME TAXES	$ 644	$ 126,368	$ 126,389

Income Taxes Reconciliation of

Income Taxes Reconciliation of the Statutory Income Tax Rate and the Company's Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the Statutory Income Tax Rate and the Company's Effective Tax Rate [Abstract]
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	$ 68,441	$ 121,085	$ 121,352
Income Tax Reconciliation, State and Local Income Taxes	2,723	5,487	4,293
Tax Cuts And Jobs Act Of 2017 Income Tax Expense Benefit	(74,738)	0	0
Income Tax Reconciliation, Other Reconciling Items	4,218	(204)	744
PROVISION FOR INCOME TAXES	$ 644	$ 126,368	$ 126,389

Income Taxes Components of inco

Income Taxes Components of income/(loss) before income tax expense/(benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income (Loss) from Continuing Operations before Income Taxes, Domestic	$ 176,853	$ 329,818	$ 331,813
Income (Loss) from Continuing Operations before Income Taxes, Foreign	18,693	16,140	14,906
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	$ 195,546	$ 345,958	$ 346,719

Income Taxes Tax Credit Carryfo

Income Taxes Tax Credit Carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets, Operating Loss Carryforwards	$ 200
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	400
Deferred Tax Assets, Capital Loss Carryforwards		$ 700
Deferred Tax Assets, Tax Credit Carryforwards	700
Deferred Tax Assets, Charitable Contribution Carryforwards	200
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	422	0
Deferred Tax Assets, Net of Valuation Allowance	9,084	19,823
Accrued Vacation
Deferred Tax Assets, Gross	690	1,183
Deferred Tax Assets, Accrued Bonus [Member]
Deferred Tax Assets, Gross	628	9,340
State Taxes
Deferred Tax Assets, Gross	318	2,187
Accrued Property Taxes
Deferred Tax Assets, Gross	1,573	2,077
Other 1
Deferred Tax Assets, Gross	3,679	1,910
Stock Based Compensation
Deferred Tax Assets, Gross	1,983	3,126
Valuation Allowance, Operating Loss Carryforwards
Deferred Tax Assets, Gross	635	0
Prepaid Expenses
Deferred Tax Liabilities, Gross, Noncurrent	4,275	5,049
Depreciation
Deferred Tax Liabilities, Gross, Noncurrent	118,743	86,981
Foreign deferred
Deferred Tax Liabilities, Gross, Noncurrent	4,569	3,131
Total Noncurrent
Deferred Tax Liabilities, Net	127,587	95,161
Total
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	$ 118,503	$ 75,338

Income Taxes Impact of U.S. Fed

Income Taxes Impact of U.S. Federal Income Tax Reform (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax Cuts And Jobs Act Of 2017 Income Tax Expense Benefit	$ (74,738)	$ 0	$ 0

Related Party Transactions (Det

Related Party Transactions (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)ft²	Dec. 31, 2015USD ($)
Related Party Transaction [Line Items]
Area of Real Estate Property | ft²	500,000
Related Party Transaction, Amounts of Transaction		$ 0	$ 1,183
Equity Method Investment, Ownership Percentage	$ 2,300
Lease Termination
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction		$ 1,300
Game Plane, LLC
Related Party Transaction [Line Items]
Related Party, Ownership Percentage		25.00%
Related Party Transaction, Amounts of Transaction		$ 0	365
Affiliated Entity
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 200	$ 1,700	2,900
GMS Racing, LLC
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction			$ 2,500
Building 2
Related Party Transaction [Line Items]
Area of Real Estate Property | ft²		10,000
Building 1
Related Party Transaction [Line Items]
Area of Real Estate Property | ft²		70,000

Employee Benefit Plans (Details

Employee Benefit Plans (Details)	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares	Dec. 31, 2014USD ($)$ / sharesshares
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent	90.00%			25.00%
Defined Contribution Plan, Cost | $	$ 14,182,000	$ 5,768,000	$ 4,218,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized		2,000,000
Share-based compensation expense | $	13,856,000	$ 9,389,000	$ 10,474,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized | $	19,730,000
Cash-settled SARs | $	481,000
EmployeeServiceShareBasedCompensationNonvestedAwardTotalCompensationCostNotYetRecognized | $	$ 20,211,000
EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostsNotYetRecognizedPeriodForRecognition	1 year 8 months 23 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Weighted Average Volatility Rate	32.80%	33.20%	30.20%
Fair Value Assumptions, Expected Dividend Rate	1.62%	1.51%	1.47%
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSARsExercisesInPeriodTotalIntrinsicValue | $	$ 1,263,000	$ 237,000	$ 5,750,000
Proceeds from the exercise of stock options | $	$ 964,000	$ 564,000	$ 1,924,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	192,890	253,658	82,957	98,782
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares	$ 153.32	$ 146.01	$ 155.30	$ 91.15
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares	$ 165.61	$ 144.74	$ 178.68
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	125,442	224,018	47,810
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(91,338)	(43,310)	(54,825)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value | $ / shares	$ 145.08	$ 129.96	$ 83.35
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(94,872)	(10,007)	(8,810)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value | $ / shares	$ 157.95	$ 158.74	$ 130.35
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value | $	$ 13,252,000	$ 5,629,000	$ 4,570,000
Shares Held in Employee Stock Option Plan, Allocated				1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date				10.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount | $				$ 25,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans	18,498	13,400	8,306
Stock Compensation Plan [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Share-based compensation expense | $	$ 14,000,000	$ 9,600,000	$ 10,600,000
Restricted Stock
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 8 months 27 days
Stock Appreciation Rights (SARs)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	80,464	104,608	131,741	119,513
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 7 months 13 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		15,000	77,396
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | $ / shares		$ 146.03	$ 181.47
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	(14,682)	(10,083)	(21,722)
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price | $ / shares	$ 177.60	$ 170.21	$ 135.16
Exercised (in Shares)	(9,462)	(32,050)	(43,446)
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price | $ / shares	$ 106	$ 89.19	$ 80.10
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSARsOutstandingIntrinsicValue | $	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number	74,122
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price | $ / shares	$ 155.02
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	2 years 1 month 21 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	57,433
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price | $ / shares	$ 150.74
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price | $ / shares	$ 155.13	$ 153.86	$ 136.13	$ 86.23
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 1 month 17 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	1 year 10 months 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | $	$ 230,000
Stock Options
Fair Value Inputs, Assets, Quantitative Information [Line Items]
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSARsOutstandingNumber		43,589	48,781	88,749
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSARsOutstandingWeightedAverageExercisePrice | $ / shares		84.04	86.65	69.43
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period			(3,000)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period			3.50
Exercised (in Shares)	(16,014)	(5,192)	(36,968)
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price | $ / shares	$ 60.20	$ 108.59	$ 52.06
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsSARsOutstandingWeightedAverageRemainingContractualTerm2		1 year 6 months 18 days	2 years 7 months 13 days	3 years 3 months 15 days
ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsSARsOutstandingIntrinsicValue | $		$ 3,590,000	$ 3,960,000	$ 7,180,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number	27,575
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price | $ / shares	$ 97.88
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	8 months 19 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $	$ 1,568,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number	27,575
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price | $ / shares	$ 97.88
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term	8 months 19 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value | $	$ 1,568,000
Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Risk Free Interest Rate	0.60%	0.40%	0.30%	0.40%
Fair Value Assumptions, Risk Free Interest Rate	0.60%	0.40%	0.30%	0.40%
Minimum | Stock Appreciation Rights (SARs)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Expected Term	2 months 12 days	3 months 18 days	3 months 18 days	1 year 4 months 24 days
Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Risk Free Interest Rate	1.90%	1.50%	1.20%	0.90%
Fair Value Assumptions, Risk Free Interest Rate	1.90%	1.50%	1.20%	0.90%
Maximum | Stock Appreciation Rights (SARs)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Expected Term	1 year 10 months 24 days	3 years 1 month 6 days	2 years 6 months	2 years 6 months
Employee
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	5.00%
Pilot
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	10.00%

Employee Benefit Plans Employee

Employee Benefit Plans Employee Stock Purchase Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Postemployment Benefits [Abstract]
Shares Held in Employee Stock Option Plan, Allocated				1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date				10.00%
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent	90.00%			25.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount				$ 25,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans	18,498	13,400	8,306

Commitments and Contingencies (

Commitments and Contingencies (Detail)	1 Months Ended	12 Months Ended
	Feb. 02, 2018Aircraft	Dec. 31, 2017USD ($)ft²Aircraftpurchase_agreement	Dec. 31, 2016USD ($)ft²Aircraftpurchase_agreement	Dec. 31, 2015USD ($)purchase_agreement	Jan. 31, 2018aircraft
Long-term Purchase Commitment [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		$ 7,455,000
Operating Leases, Rent Expense		9,000,000	$ 8,100,000	$ 7,870,000
Aircraft lease rentals		$ 3,098,000	$ 924,000	2,326,000
Sub-Service Expense				$ 2,100,000
Number Of Aircraft Committed To Purchase | Aircraft		16
Commitments to Lease Aircraft		13
Area of Real Estate Property | ft²		500,000
Operating Leases, Future Minimum Payments, Due in Two Years		$ 6,592,000
Operating Leases, Future Minimum Payments, Due in Three Years		4,716,000
Operating Leases, Future Minimum Payments, Due in Four Years		2,768,000
Operating Leases, Future Minimum Payments, Due in Five Years		1,071,000
Operating Leases, Future Minimum Payments, Due Thereafter		5,824,000
Other Commitment, Due in Next Twelve Months		11,336,000
Purchase Obligation, Due in Next Twelve Months		150,264,000
Purchase Obligation, Due in Second Year		97,310,000
Purchase Obligation, Due in Third Year		66,560,000
Purchase Obligation, Due in Fourth Year		32,375,000
Purchase Obligation, Due in Fifth Year		29,155,000
Purchase Obligation, Due after Fifth Year		198,450,000
Contractual Obligation, Due in Second Year		10,454,000
Other Commitment, Due in Third Year		5,224,000
Other Commitment, Due in Fourth Year		63,000
Other Commitment, Due in Fifth Year		0
Other Commitment, Due after Fifth Year		0
Contractual Obligation, Due in Third Year		76,500,000
Contractual Obligation, Due in Fourth Year		35,206,000
Contractual Obligation, Due in Fifth Year		30,226,000
Contractual Obligation, Due after Fifth Year		204,274,000
Contractual Obligation, Due in Next Fiscal Year		169,055,000
Contractual Obligation, Due in Second Year		$ 114,356,000
Airbus A320 Aircraft Series
Long-term Purchase Commitment [Line Items]
Number Of Aircraft Committed To Purchase | Aircraft		6
Aircraft scheduled to be acquired | Aircraft		7
Airbus A320 Aircraft Series | 2017 Purchase Agreements
Long-term Purchase Commitment [Line Items]
Aircraft acquired | Aircraft		4
Airbus A320 Aircraft Series | 2016 Purchase Agreements
Long-term Purchase Commitment [Line Items]
Aircraft acquired | Aircraft		13
Airbus A320 Aircraft Series | Capital Addition Purchase Commitments
Long-term Purchase Commitment [Line Items]
Commitments To Purchase Aircraft Table [Text Block] | purchase_agreement		3	4	1
Number Of Aircraft Committed To Purchase | Aircraft		4	27
Airbus A320 Aircraft Series New Manufacture | Capital Addition Purchase Commitments
Long-term Purchase Commitment [Line Items]
Number Of Aircraft Committed To Purchase | Aircraft			12
Building 2
Long-term Purchase Commitment [Line Items]
Area of Real Estate Property | ft²			10,000
Subsequent Event
Long-term Purchase Commitment [Line Items]
Number Of Aircraft Committed To Purchase | aircraft					1
Subsequent Event | Airbus A320 Aircraft Series
Long-term Purchase Commitment [Line Items]
Aircraft scheduled to be acquired | Aircraft	2

Valuation and Qualifying Acco65

Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 7,205	$ 4,607	$ 3,003
Changes Charged to Statement of Income Account	6,551	2,598	1,604
Balance at End of Year	13,756	$ 7,205	$ 4,607
MD-80 Aircraft | Reserve For Impairment On Equipment [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at End of Year	$ 2,000

Subsequent Events (Details)

Subsequent Events (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2017USD ($)Aircraft$ / shares	Dec. 31, 2016USD ($)$ / shares	Dec. 31, 2015USD ($)$ / shares	Jan. 31, 2018aircraft
Subsequent Event [Line Items]
Number Of Aircraft Committed To Purchase | Aircraft		16
Debt Instrument, Collateral		$ 497,540	$ 321,160	$ 121,000
Debt Instrument, Collateral	12
Cash dividends (per Share) | $ / shares		$ 2.80	$ 2.40	$ 2.75
Secured Long-term Debt, Noncurrent		$ 1,164,892	$ 808,274
Subsequent Event
Subsequent Event [Line Items]
Number Of Aircraft Committed To Purchase | aircraft					1