Spirit Airlines (SAVE1) 10-K 18 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Billions, except Share data, unless otherwise specified	Dec. 31, 2014	Feb. 06, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Entity Registrant Name	SPIRIT AIRLINES, INC.
Entity Central Index Key	1498710
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$4.60
Entity Common Stock, Shares Outstanding		72,775,915

Statements_Of_Operations

Statements Of Operations (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating revenues:
Passenger	$1,144,972	$986,018	$782,792
Non-ticket	786,608	668,367	535,596
Total operating revenues	1,931,580	1,654,385	1,318,388
Operating expenses:
Aircraft fuel	612,909	551,746	471,763
Salaries, wages and benefits	313,988	262,150	218,919
Aircraft rent	195,827	169,737	143,572
Landing fees and other rents	105,115	83,604	68,368
Distribution	74,823	67,481	56,668
Maintenance, materials and repairs	73,956	60,143	49,460
Depreciation and amortization	46,971	31,947	15,256
Other operating	149,675	144,586	127,886
Loss on disposal of assets	3,008	525	956
Special charges (credits)	45	174	-8,450
Total operating expenses	1,576,317	1,372,093	1,144,398
Operating income	355,263	282,292	173,990
Other (income) expense:
Interest expense	2,747	214	1,350
Capitalized interest	-2,747	-214	-1,350
Interest income	-336	-401	-925
Other expense	2,605	283	331
Total other (income) expense	2,269	-118	-594
Income before income taxes	352,994	282,410	174,584
Provision for income taxes	127,530	105,492	66,124
Net income	$225,464	$176,918	$108,460
Basic earnings per share (in dollars per share)	$3.10	$2.44	$1.50
Diluted earnings per share (in dollars per share)	$3.08	$2.42	$1.49

Statements_of_Comprehensive_In

Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income	$225,464	$176,918	$108,460
Unrealized gain (loss) on interest rate derivative instruments, net of deferred taxes of $423, $0, and $0	-718	0	0
Other Comprehensive Income (Loss)	-718	0	0
Comprehensive Income	$224,746	$176,918	$108,460

Statements_of_Comprehensive_In1

Statements of Comprehensive Income (Parentheticals) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Unrealized gain (loss) on interest rate derivative instruments, deferred tax	$423	$0	$0

Balance_Sheets

Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$632,784	$530,631
Accounts receivable, net	22,685	23,246
Deferred income taxes	9,643	16,243
Prepaid expenses and other current assets	66,029	78,955
Total current assets	731,141	649,075
Property and equipment:
Flight equipment	204,462	12,744
Ground and other equipment	57,012	48,090
Less accumulated depreciation	-36,099	-25,221
Total property and equipment	225,375	35,613
Deposits on flight equipment purchase contracts	242,881	157,669
Aircraft maintenance deposits	213,147	161,484
Deferred heavy maintenance, net	123,108	125,288
Other long-term assets	67,329	51,636
Total assets	1,602,981	1,180,765
Current liabilities:
Accounts payable	13,402	23,104
Air traffic liability	188,870	167,627
Current maturities of long-term debt	10,431	0
Other current liabilities	152,921	145,262
Total current liabilities	365,624	335,993
Long-term debt less current maturities	135,817	0
Long-term deferred income taxes	76,010	48,916
Deferred gains and other long-term liabilities	22,455	26,739
Shareholders’ equity:
Common stock: Common stock, $0.0001 par value, 240,000,000 shares authorized at December 31, 2014 and 2013, respectively; 72,907,827 and 72,774,920 issued and 72,775,685 and 72,670,673 outstanding as of December 31, 2014 and 2013, respectively	7	7
Additional paid-in-capital	526,173	515,331
Treasury stock, at cost: 132,142 and 104,247 shares as of December 31, 2014 and 2013, respectively	-3,921	-2,291
Retained earnings	481,534	256,070
Accumulated other comprehensive income (loss)	-718	0
Total shareholders’ equity	1,003,075	769,117
Total liabilities and shareholders’ equity	$1,602,981	$1,180,765

Balance_Sheets_Parenthetical

Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Treasury stock, shares	132,142	104,247
Voting Common Stock
Common stock, par value (in dollars per share)	0.0001	0.0001
Common stock, shares authorized	240,000,000	240,000,000
Common stock, shares issued	72,907,827	72,774,920
Common stock, shares outstanding	72,775,685	72,670,673
Non-Voting Common Stock
Common stock, par value (in dollars per share)	0.0001	0.0001
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	0	0
Common stock, shares outstanding	0	0

Statements_of_Cash_Flows

Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities:
Net income	$225,464	$176,918	$108,460
Adjustments to reconcile net income to net cash provided by operations:
Unrealized (gains) losses on open fuel derivative contracts	0	265	46
Equity-based compensation, net	8,797	5,689	4,327
Allowance for doubtful accounts (recoveries)	-45	143	78
Amortization of deferred gains and losses and debt issuance costs	-185	-558	-830
Depreciation and amortization	46,971	31,947	15,256
Deferred income tax	34,118	12,047	29,255
Loss on disposal of assets	3,008	525	956
Gain on slot sale	0	0	-9,060
Capitalized interest	-2,747	-214	-1,350
Changes in operating assets and liabilities:
Accounts receivable	606	-461	-7,393
Prepaid maintenance reserves	-31,925	-24,058	-31,567
Long-term deposits and other assets	-48,382	-65,654	-68,248
Accounts payable	-10,034	-1,674	8,452
Air traffic liability	21,135	36,226	19,134
Other liabilities	13,731	24,235	46,115
Net cash provided by operating activities	260,512	195,376	113,631
Investing activities:
Proceeds from sale of property and equipment	0	0	14
Proceeds from sale of slots	0	0	9,060
Pre-delivery deposits for flight equipment, net of refunds	-115,802	-70,288	-12,626
Purchase of property and equipment	-186,569	-19,812	-23,771
Net cash used in investing activities	-302,371	-90,100	-27,323
Financing activities:
Proceeds from issuance of long-term debt	148,000	0	0
Proceeds from stock options exercised	174	852	469
Payments on debt and capital lease obligations	-1,233	0	0
Proceeds from sale and leaseback transactions	7,200	6,900	12,540
Payments to pre-IPO shareholders pursuant to tax receivable agreement	-5,643	0	-26,905
Excess tax benefits from equity-based compensation	1,871	1,927	2,098
Repurchase of common stock	-1,630	-1,140	-1,022
Debt issuance costs	-4,727	0	0
Net cash provided by financing activities	144,012	8,539	-12,820
Net increase in cash and cash equivalents	102,153	113,815	73,488
Cash and cash equivalents at beginning of period	530,631	416,816	343,328
Cash and cash equivalents at end of period	632,784	530,631	416,816
Cash payments for:
Interest (net of capitalized interest)	0	0	0
Taxes	89,104	85,705	40,204
Non-cash transactions:
Liability and equity related to tax receivable agreement	0	-2,336	-1,497
Capital expenditures funded by capital lease borrowings	($173)	($3,234)	$0

Statements_of_Shareholders_Equ

Statements of Shareholders’ Equity (USD $)	Total	Common Stock	Common Stock	Additional Paid-In Capital	Treasury Stock	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)
In Thousands, unless otherwise specified		Voting Common Stock	Non- Voting Common Stock
Balance at Dec. 31, 2011	$466,706	$6	$1	$496,136	($129)	($29,308)	$0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment to liability recorded under Tax Receivable Agreement	1,497			1,497
Share-based compensation	4,327			4,327
Repurchase of common stock	-1,022				-1,022
Proceeds from options exercised	469			469
Excess tax benefits from share-based compensation	2,098			2,098
Unrealized gain (loss) from cash flow hedges, net of tax	0
Net income	108,460					108,460
Balance at Dec. 31, 2012	582,535	6	1	504,527	-1,151	79,152	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment to liability recorded under Tax Receivable Agreement	2,336			2,336
Share-based compensation	5,689			5,689
Repurchase of common stock	-1,140				-1,140
Conversion of non-voting common stock to common stock	0	1	-1
Proceeds from options exercised	852			852
Excess tax benefits from share-based compensation	1,927			1,927
Unrealized gain (loss) from cash flow hedges, net of tax	0
Net income	176,918					176,918
Balance at Dec. 31, 2013	769,117	7	0	515,331	-2,291	256,070	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	8,797			8,797
Repurchase of common stock	-1,630				-1,630
Proceeds from options exercised	174			174
Excess tax benefits from share-based compensation	1,871			1,871
Unrealized gain (loss) from cash flow hedges, net of tax	-718						-718
Net income	225,464					225,464
Balance at Dec. 31, 2014	$1,003,075	$7	$0	$526,173	($3,921)	$481,534	($718)

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies
	Basis of Presentation
	Spirit Airlines, Inc. (Spirit or the Company) headquartered in Miramar, Florida, is an ultra low-cost, low-fare airline that provides affordable travel opportunities principally throughout the domestic United States, the Caribbean and Latin America. The Company manages operations on a system-wide basis due to the interdependence of its route structure in the various markets served. As only one service is offered (i.e., air transportation), management has concluded there is only one reportable segment.
	Certain prior period amounts have been reclassified to conform to the current year's presentation.
	Use of Estimates
	The preparation of financial statements in accordance with generally accepted accounting principles in the United States of America requires the Company's management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The Company's estimates and assumptions are based on historical experience and changes in the business environment. However, actual results may differ from estimates under different conditions, sometimes materially. Critical accounting policies and estimates are defined as those that both (i) are most important to the portrayal of the Company's financial condition and results and (ii) require management's most subjective judgments. The Company's most critical accounting policies and estimates are described below.
	Cash and Cash Equivalents
	The Company considers all highly liquid investments with maturities of less than three months at the date of acquisition to be cash equivalents. Investments included in this category primarily consist of money market funds. Cash and cash equivalents are stated at cost, which approximates fair value.
	Restricted Cash
	Restricted cash, when reported, consists of funds held by credit card processors as collateral for future travel paid with a credit card. As of December 31, 2014 and 2013, the Company held no restricted cash.
	Accounts Receivable
	Accounts receivable primarily consist of amounts due from credit card processors associated with the sales of tickets and amounts due from counterparties associated with fuel derivative instruments which have settled. The Company records an allowance for doubtful accounts for amounts not expected to be collected. The Company estimates the allowance based on historical write offs as well as aging trends. The allowance for doubtful accounts was immaterial as of December 31, 2014 and 2013.
	In addition, the provision for doubtful accounts and write-offs for 2014, 2013 and 2012 were each immaterial.
	Property and Equipment
	Property and equipment is stated at cost, less accumulated depreciation and amortization. Depreciation of operating property and equipment is computed using the straight-line method applied to each unit of property. Residual values for aircraft, major spare rotable parts, avionics and assemblies are estimated to be 10%. Property under capital leases and related obligations are initially recorded at an amount equal to the present value of future minimum lease payments computed using the Company's incremental borrowing rate or, when known, the interest rate implicit in the lease. Amortization of property under capital leases is on a straight-line basis over the lease term and is included in depreciation and amortization expense.
	The depreciable lives used for the principal depreciable asset classifications are:
		Estimated Useful Life
	Aircraft	25 years
	Spare rotables and flight assemblies	7 to 15 years
	Other equipment and vehicles	5 to 7 years
	Internal use software	3 to 10 years
	Capital lease	Lease term
	Leasehold improvements	Lesser of lease term or estimated useful life of the improvement
	As of December 31, 2014, the Company had 4 aircraft capitalized within flight equipment with depreciable lives of 25 years and 61 aircraft financed through operating leases with terms of 3 to 15 years. All spare engines are financed through operating leases with terms of 7 to 12 years.
	In the third quarter of 2014, the Company purchased $13.5 million of rotable spare inventory which was previously rented. The cost to rent this inventory was recorded as maintenance, materials and repairs within the statement of operations. As a result of the purchase, the inventory was capitalized and the cost is amortized over the remaining useful life of the assets. The amortization is recorded as depreciation and amortization within the statement of operations.
	The following table illustrates the components of depreciation and amortization expense:
		Year Ended December 31,
		2014			2013			2012
		(in thousands)
	Depreciation	$	11,169		$	8,340		$	6,156
	Amortization of heavy maintenance	35,802			23,607			9,100
	Total depreciation and amortization	$	46,971		$	31,947		$	15,256
	The Company capitalizes certain internal and external costs associated with the acquisition and development of internal-use software for new products, and enhancements to existing products, that have reached the application development stage and meet recoverability tests. Capitalized costs include external direct costs of materials and services utilized in developing or obtaining internal-use software, and labor cost for employees who are directly associated with, and devote time, to internal-use software projects. Capitalized computer software, included as a component of ground and other equipment in the accompanying balance sheets, net of accumulated depreciation, was $7.4 million and $8.1 million at December 31, 2014 and 2013, respectively.
	Amortization of capitalized software costs is charged to depreciation on a straight-line method basis. Amortization of capitalized software costs was $3.5 million, $3.7 million and $3.2 million for the years ended 2014, 2013 and 2012, respectively. The Company placed in service internal-use software of $2.7 million, $7.0 million and $2.3 million, during the years ended 2014, 2013 and 2012, respectively.
	Measurement of Asset Impairments
	The Company records impairment charges on long-lived assets used in operations when events and circumstances indicate that the assets may be impaired, the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets, and the net book value of the assets exceeds their estimated fair value. In making these determinations, the Company uses certain assumptions, including, but not limited to: (i) estimated fair value of the assets; and (ii) estimated, undiscounted future cash flows expected to be generated by these assets, which are based on additional assumptions such as asset utilization, length of service the asset will be used in the Company’s operations, and estimated salvage values.
	Passenger Revenue Recognition
	Tickets sold are initially deferred as “air traffic liability.” Passenger revenue is recognized at time of departure when transportation is provided. A nonrefundable ticket expires at the date of scheduled travel and is recognized as revenue at the date of scheduled travel.
	Customers may elect to change their itinerary prior to the date of departure. A service charge is assessed and recognized on the date the change is initiated and is deducted from the face value of the original purchase price of the ticket, and the original ticket becomes invalid. The amount remaining after deducting the service charge is called a credit shell which expires 60 days from the date the credit shell is created and can be used towards the purchase of a new ticket and the Company’s other service offerings. The amount of credits expected to expire is recognized as revenue upon issuance of the credit and is estimated based on historical experience. Estimating the amount of credits that will go unused involves some level of subjectivity and judgment.
	The Company is also required to collect certain taxes and fees from customers on behalf of government agencies and airports and remit these back to the applicable governmental entity or airport on a periodic basis. These taxes and fees include U.S. federal transportation taxes, federal security charges, airport passenger facility charges and international arrival and departure taxes. These items are collected from customers at the time they purchase their tickets, but are not included in passenger revenue. The Company records a liability upon collection from the customer and relieves the liability when payments are remitted to the applicable governmental agency or airport.
	Frequent Flier Program
	Flown Miles. The Company records unrecognized revenue for mileage credits earned by passengers under its FREE SPIRIT program, including mileage credits for members with an insufficient number of mileage credits to earn an award, based on the estimated incremental cost of providing free travel for credits that are expected to be redeemed. Incremental costs include fuel, insurance, security, ticketing and facility charges reduced by an estimate of fees required to be paid by the passenger when redeeming the award.
	Affinity Card Program. Under the Company's affinity card program, funds received for the marketing of a co-branded Spirit credit card and delivery of award miles are accounted for as a mulitple-deliverable arrangement. At the inception of the arrangement, the Company evaluated all deliverables in the arrangement to determine whether they represent separate units of accounting. The Company determined the arrangement had three separate units of accounting: (i) travel miles to be awarded, (ii) licensing of brand and access to member lists and (iii) advertising and marketing efforts. Arrangement consideration was allocated based on relative selling price. At inception of the arrangement, the Company established the relative selling price for all deliverables that qualified for separation. The manner in which the selling price was established was based on a hierarchy of evidence that the Company considered. Total arrangement consideration was then allocated to each deliverable on the basis of the deliverable’s relative selling price. In considering the hierarchy of evidence, the Company first determined whether vendor specific objective evidence of selling price or third-party evidence of selling price existed. It was determined by the Company that neither vendor specific objective evidence of selling price nor third-party evidence existed due to the uniqueness of the Company’s program. As such, the Company developed its best estimate of the selling price for all deliverables. For the award miles, the Company considered a number of entity-specific factors when developing the best estimate of the selling price including the number of miles needed to redeem an award, average fare of comparable segments, breakage, restrictions and other charges. For licensing of brand and access to member lists, the Company considered both market-specific factors and entity-specific factors including general profit margins realized in the marketplace/industry, brand power, market royalty rates and size of customer base. For the advertising element, the Company considered market-specific factors and entity-specific factors, including the Company’s internal costs (and fluctuations of costs) of providing services, volume of marketing efforts and overall advertising plan. Consideration allocated based on the relative selling price to both brand licensing and advertising elements is recognized as revenue when earned and recorded in non-ticket revenue. Consideration allocated to award miles is deferred and recognized ratably as passenger revenue over the estimated period the transportation is expected to be provided which is estimated at 14 months. The Company used entity-specific assumptions coupled with the various judgments necessary to determine the selling price of a deliverable in accordance with the required selling price hierarchy. Changes in these assumptions could result in changes in the estimated selling prices. Determining the frequency to reassess selling price for individual deliverables requires significant judgment. As of December 31, 2014, there have been no changes in either the selling price or the method or assumptions used to determine selling price for any of the identified units of accounting that would have a significant effect on the allocation of consideration.
	The following table illustrates total cash proceeds received from the sale of mileage credits and the portion of such proceeds recognized in revenue immediately as marketing component:
		Consideration received from credit card mile programs			Portion of proceeds recognized immediately as marketing component
	Year Ended	(in thousands)
	December 31, 2014	$	33,819		$	28,140
	December 31, 2013	28,496			23,124
	December 31, 2012	24,938			20,998
	Total unrecognized revenue from future FREE SPIRIT award redemptions and the sale of mileage credits was $2.8 million and $2.6 million at December 31, 2014 and 2013, respectively. These balances are recorded as a component of air traffic liability in the accompanying balance sheets.
	Non-ticket Revenue Recognition
	Non-ticket revenues are generated from air travel-related services for baggage, bookings through the Company’s call center or third-party vendors, advance seat selection, itinerary changes and loyalty programs. Non-ticket revenues also consist of services not directly related to providing transportation such as the FREE SPIRIT affinity credit card program, $9 Fare Club and the sale of advertising to third parties on Spirit’s website and on board aircraft.
	The following table summarizes the primary components of non-ticket revenue and the revenue recognition method utilized for each service or product:
			Year Ended December 31,
	Non-ticket revenue	Recognition method	2014			2013			2012
			(in thousands)
	Baggage	Time of departure	$	318,103		$	275,958		$	217,536
	Passenger usage fee	Time of departure	221,992			188,911			149,577
	Advance seat selection	Time of departure	76,270			59,241			48,956
	Service charges for changes and cancellations	When itinerary is changed	38,388			32,546			27,762
	Other		131,855			111,711			91,765
	Non-ticket revenue		$	786,608		$	668,367		$	535,596
	Charges for services recognized at time of departure are initially recorded as a liability until time of departure. The passenger usage fee is charged for tickets sold through the Company’s primary sales distribution channels. The primary sales distribution channels for which passenger usage fees are charged include sales through the Company’s website, sales through the third-party provided call center and sales through travel agents; the Company does not charge a passenger usage fee for sales made at its airport ticket counters. Other non-ticket revenues include revenues from other air related charges as well as non-air related charges. Other air related charges include optional services and products provided to passengers such as on-board products, travel insurance and use of the Company’s call center or travel agents, among others. Non-air related charges primarily consist of revenues from advertising on the Company’s aircraft and website, the Company’s $9 Fare Club subscription-based membership program and the Company’s FREE SPIRIT affinity credit card program.
	Airframe and Engine Maintenance
The Company accounts for heavy maintenance and major overhaul and repair under the deferral method whereby the cost of heavy maintenance and major overhaul and repair is deferred and amortized until the earlier of the end of the remaining lease term or until the next scheduled heavy maintenance event.
Amortization of heavy maintenance and major overhaul costs is charged to depreciation and amortization expense and was $35.8 million, $23.6 million and $9.1 million for the years ended 2014, 2013 and 2012, respectively. During the years ended 2014, 2013 and 2012, the Company deferred $33.6 million, $70.8 million and $61.6 million, respectively, of costs for heavy maintenance. At December 31, 2014 and 2013, the Company had deferred heavy maintenance balance of $198.9 million and $165.3 million, and accumulated heavy maintenance amortization of $75.8 million and $40.0 million, respectively.
On October 15, 2013, a Company aircraft experienced an engine failure resulting in damage to the airframe and engine. In 2013, the Company expensed the insurance deductible related to this incident of approximately $0.8 million. As of December 31, 2014, the Company received insurance proceeds for a portion of the damage incurred. During 2014, the Company received a new replacement engine from the manufacturer in exchange for a $2.3 million payment to the manufacturer which was expensed within maintenance, materials and repairs in the statement of operations for the twelve months ended December 31, 2014.
The Company outsources certain routine, non-heavy maintenance functions under contracts that require payment on a utilization basis, such as flight hours. Costs incurred for maintenance and repair under flight hour maintenance contracts, where labor and materials price risks have been transferred to the service provider, are expensed based on contractual payment terms. All other costs for routine maintenance of the airframes and engines are charged to expense as performed.
The table below summarizes the extent to which the Company’s maintenance costs are rate capped due to flight hour maintenance contracts:
	Year Ended December 31,
	2014			2013			2012
	(in thousands)
Flight hour-based maintenance expense	$	35,675		$	30,322		$	25,748
Non-flight hour-based maintenance expense	38,281			29,821			23,712
Total maintenance, materials and repairs	$	73,956		$	60,143		$	49,460
Leased Aircraft Return Costs
The Company's aircraft lease agreements often contain provisions that require the Company to return aircraft airframes and engines to the lessor in a certain maintenance condition or pay an amount to the lessor based on the airframe and engine's actual return condition. Lease return costs, which could include cost to perform maintenance to airframes and engines to acceptable conditions prior to return, will be recognized as expense beginning when it is probable that such costs will be incurred and they can be estimated. Incurrence of lease return costs becomes probable and the amount of those costs can typically be estimated near the end of the lease term (that is, after the aircraft has completed its last maintenance cycle prior to being returned). The Company will evaluate all lease return conditions after the second to last maintenance event as it relates to the respective component or airframe from the lease return. If at this point it becomes both probable and estimable that a return cost will be incurred, the Company will accrue the cost on a straight-line basis as contingent rent through the remaining lease term. Return costs are recorded as a component of supplemental rent.
Aircraft Fuel
Aircraft fuel expense includes jet fuel and associated “into-plane” costs, taxes, and oil, and realized and unrealized gains and losses associated with fuel derivative contracts.
Derivative Instruments
The Company accounts for derivative financial instruments at fair value and recognizes them in the balance sheet in prepaid expenses and other current assets or other current liabilities. For derivatives designated as cash flow hedges, changes in fair value of the derivative are generally reported in other comprehensive income and are subsequently reclassified into earnings when the hedged item affects earnings. On October 23, 2014, the Company entered into six forward interest rate swaps that fix the benchmark interest rate component of the forecasted interest payments on the debt related to three Airbus A321 aircraft with expected delivery dates ranging from July 2015 to September 2015 to limit the Company's exposure to changes in the benchmark interest rate in the period from the trade date through the aircraft delivery date. These interest rate swaps are designated as cash flow hedges. As a result, changes in the fair value of such derivatives are recorded within other accumulated comprehensive income.
For the years ended 2014, 2013 and 2012, the Company did not hold fuel derivative instruments that were designated as cash flow hedges for accounting purposes. As a result, changes in the fair value of such fuel derivative contracts were recorded within aircraft fuel expense in the accompanying statements of operations. These amounts include both realized gains and losses and mark-to-market adjustments of the fair value of unsettled derivative instruments at the end of each period. See Note 12 for additional information.
Advertising
The Company expenses advertising and the production costs of advertising as incurred. Marketing and advertising expenses of $3.0 million, $2.1 million and $2.4 million for the years ended 2014, 2013 and 2012, respectively, were recorded within distribution expense in the statement of operations.
Income Taxes
The Company accounts for income taxes using the liability method. The Company records a valuation allowance to reduce the deferred tax assets reported if, based on the weight of the evidence, it is more likely than not that some portion or all of the deferred tax assets will be not realized. As of December 31, 2014 and 2013, the Company had no valuation allowance recorded against any deferred tax assets.
Stock-Based Compensation
The Company recognizes cost of employee services received in exchange for awards of equity instruments based on the fair value of each instrument at the date of grant. Compensation expense is recognized on a straight-line basis over the period during which an employee is required to provide service in exchange for an award. The Company has issued and outstanding restricted stock awards, stock option awards and performance share awards. Restricted stock awards are valued at the fair value of the shares on the date of grant. To the extent a market price was not available, the fair value of stock awards was estimated using a discounted cash flow analysis based on management’s estimates of revenue, driven by assumed market growth rates and estimated costs as well as appropriate discount rates. These estimates are consistent with the plans and estimates that management uses to manage the Company’s business. The fair value of share option awards is estimated on the date of grant using the Black-Scholes valuation model. The fair value of performance share awards is estimated through the use of a Monte Carlo simulation model. See Note 8 for additional information.
Concentrations of Risk
The Company’s business has been, and may continue to be, adversely affected by increases in the price of aircraft fuel, the volatility of the price of aircraft fuel, or both. Aircraft fuel was the Company’s single largest expenditure representing approximately 39%, 40% and 41% of total operating expenses in 2014, 2013 and 2012, respectively.
The Company’s operations are largely concentrated in the southeast United States with Fort Lauderdale being the highest volume fueling point in the system. Gulf Coast Jet indexed fuel is the basis for a substantial majority of the Company’s fuel consumption. Any disruption to the oil production or refinery capacity in the Gulf Coast, as a result of weather or any other disaster, or disruptions in supply of jet fuel, dramatic escalations in the costs of jet fuel and/or the failure of fuel providers to perform under fuel arrangements for other reasons could have a material adverse effect on the Company’s financial condition and results of operations.
The Company’s operations will continue to be vulnerable to weather conditions (including hurricane season or snow and severe winter weather), which could disrupt service, create air traffic control problems, decrease revenue and increase costs.
Due to the relatively small size of the fleet and high utilization rate, the unavailability of one or more aircraft and resulting reduced capacity could have a material adverse effect on the Company’s business, results of operations and financial condition.
As of December 31, 2014, the Company had four union-represented employee groups that together represented approximately 67% of all employees. As of December 31, 2013, the Company had three union-represented employee groups that together represented approximately 59% of all employees. A strike or other significant labor dispute with the Company’s unionized employees is likely to adversely affect the Company’s ability to conduct business. Additional disclosures are included in Note 15.

Recent_Accounting_Developments

Recent Accounting Developments	12 Months Ended
	Dec. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Developments	Recent Accounting Developments
	In May 2014, the Financial Accounting Standards Board (the FASB) issued Accounting Standards Update (ASU) No. 2014-09, (ASU 2014-09), "Revenue from Contracts with Customers." The objective of ASU 2014-09 is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and will supersede most of the existing revenue recognition guidance, including industry-specific guidance. The core principle of ASU 2014-09 is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying the new guidance, an entity will (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the contract's performance obligations; and (5) recognize revenue when (or as) the entity satisfies a performance obligation. ASU 2014-09 applies to all contracts with customers except those that are within the scope of other topics in the FASB Accounting Standards Codification. The new guidance is effective for annual reporting periods (including interim periods within those periods) beginning after December 15, 2016 for public companies. Early adoption is not permitted. Entities have the option of using either a full retrospective or modified approach to adopt ASU 2014-09. The Company is currently evaluating the new guidance and has not determined the impact this standard may have on its financial statements nor decided upon the planned method of adoption. While the Company is still evaluating the impact, it expects the accounting for its frequent flier program and certain ancillary fees to change.

Special_Charges_and_Credits

Special Charges and Credits	12 Months Ended
	Dec. 31, 2014
Special Charges and Credits [Abstract]
Special Charges and Credits	Special Charges and Credits
	Slot Transaction and Restructuring
	In 2012, the Company sold four permanent air carrier slots at Ronald Reagan National Airport (DCA) to another airline for $9.1 million. The Company recognized the $9.1 million gain within special charges (credits) in the third quarter of 2012, the period in which the FAA operating restriction lapsed and written confirmation of the slot transfer was received by the buyer from the FAA.

Letters_of_Credit

Letters of Credit	12 Months Ended
	Dec. 31, 2014
Financial Instruments Pledged as Collateral [Abstract]
Letters of Credit	Letters of Credit
	In connection with agreements with certain airports, the Company is required to post letters of credit, which totaled $0.2 million as of both December 31, 2014 and 2013. The issuing banks require the Company deposit funds at those banks to cover the amounts that could be drawn under the letters of credit. These funds are generally invested in money market accounts and are classified as long-term assets within other long-term assets. Additionally, as of December 31, 2014, the Company had a $25.1 million unsecured standby letter of credit facility, of which $10.3 million had been drawn upon for issued letters of credit to airports and insurance underwriters.

Credit_Card_Processing_Arrange

Credit Card Processing Arrangements	12 Months Ended
	Dec. 31, 2014
Credit Card Processing Arrangements [Abstract]
Credit Card Processing Arrangements	Credit Card Processing Arrangements
	The Company has agreements with organizations that process credit card transactions arising from the purchase of air travel, baggage charges and other ancillary services by customers. As it is standard in the airline industry, the Company's contractual arrangements with credit card processors permit them, under certain circumstances, to retain a holdback or other collateral, which the Company records as restricted cash, when future air travel and other future services are purchased via credit card transactions. The required holdback is the percentage of the Company's overall credit card sales that its credit card processors hold to cover refunds to customers if the Company fails to fulfill its flight obligations.
	The Company's credit card processors do not require the Company to maintain cash collateral provided that the Company continues to satisfy certain liquidity and other financial covenants. Failure to meet these covenants would provide the processors the right to place a holdback, resulting in a commensurate reduction of unrestricted cash. As of December 31, 2014 and 2013, the Company continued to be in compliance with its credit card processing agreements, and the processors were holding back $0 of remittances.
	The maximum potential exposure to cash holdbacks by the Company's credit card processors, based upon advance ticket sales and $9 Fare Club memberships as of December 31, 2014 and 2013, was $217.1 million and $188.6 million, respectively.

Accrued_Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
Accrued Liabilities	Accrued Liabilities
	Accrued liabilities included in other current liabilities as of December 31, 2014 and 2013 consist of the following:
		As of December 31,
		2014		2013
		(in thousands)
	Federal excise and other passenger taxes and fees payable	$	42,628	$	26,979
	Salaries and wages	34,209		26,174
	Airport expenses	21,726		17,109
	Aircraft maintenance	16,127		36,165
	Aircraft and facility rent	10,089		7,993
	Fuel	9,508		13,819
	Federal and state income tax payable	3,286		794
	Tax Receivable Agreement	—		5,643
	Other	15,348		10,586
	Other current liabilities	$	152,921	$	145,262

Common_Stock_and_Preferred_Sto

Common Stock and Preferred Stock	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Common Stock and Preferred Stock	Common Stock and Preferred Stock
	The Company’s amended and restated certificate of incorporation dated June 1, 2011, authorizes the Company to issue up to 240,000,000 shares of common stock, $0.0001 par value per share, 50,000,000 shares of non-voting common stock, $0.0001 par value per share and 10,000,000 shares of preferred stock, $0.0001 par value per share. All of the Company’s issued and outstanding shares of common stock and preferred stock are duly authorized, validly issued, fully paid and non-assessable. The Company’s shares of common stock and non-voting common stock are not redeemable and do not have preemptive rights.
	Common Stock
	Dividend Rights. Holders of the Company’s common stock are entitled to receive dividends, if any, as may be declared from time to time by the Company’s board of directors out of legally available funds ratably with shares of the Company’s non-voting common stock, subject to preferences that may be applicable to any then outstanding preferred stock and limitations under Delaware law.
	Voting Rights. Each holder of the Company’s common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders, including the election of directors. The Company’s stockholders do not have cumulative voting rights in the election of directors. Accordingly, holders of a majority of the voting shares are able to elect all of the directors properly up for election at any given stockholders’ meeting.
	Liquidation. In the event of the Company’s liquidation, dissolution or winding up, holders of the Company's common stock will be entitled to share ratably with shares of the Company’s non-voting common stock in the net assets legally available for distribution to stockholders after the payment of all of the Company’s debts and other liabilities and the satisfaction of any liquidation preference granted to the holders of any then outstanding shares of preferred stock.
	Rights and Preferences. Holders of the Company’s common stock have no preemptive, conversion, subscription or other rights and there are no redemption or sinking fund provisions applicable to the Company’s common stock. The rights, preferences and privileges of the holders of the Company’s common stock are subject to and may be adversely affected by, the rights of the holders of shares of any series of the Company’s preferred stock that the Company may designate in the future.
	Non-Voting Common Stock
	Dividend Rights. Holders of the Company’s non-voting common stock are entitled to receive dividends, if any, as may be declared from time to time by the Company’s board of directors out of legally available funds ratably with shares of the Company’s common stock, subject to preferences that may be applicable to any then outstanding preferred stock and limitations under Delaware law.
	Voting Rights. Shares of the Company’s non-voting common stock are not entitled to vote on any matters submitted to a vote of the stockholders, including the election of directors, except to the extent required under Delaware law.
	Conversion Rights. Shares of the Company’s non-voting common stock will be convertible on a share-for-share basis into common stock at the election of the holder subject to the Company remaining in compliance with applicable foreign ownership limitations.
	Liquidation. In the event of the Company’s liquidation, dissolution or winding up, holders of the Company’s non-voting common stock will be entitled to share ratably with shares of the Company’s common stock in the net assets legally available for distribution to stockholders after the payment of all of the Company’s debts and other liabilities and the satisfaction of any liquidation preference granted to the holders of any then outstanding shares of preferred stock.
	Rights and Preferences. Holders of the Company’s non-voting common stock have no preemptive, subscription or other rights, and there are no redemption or sinking fund provisions applicable to the Company’s common stock. The rights, preferences and privileges of the holders of the Company’s common stock are subject to and may be adversely affected by, the rights of the holders of shares of any series of the Company’s preferred stock that the Company may designate in the future.
	On December 7, 2011, the Company entered into a Stock Distribution Agreement with Indigo Miramar LLC and its members. Pursuant to the Stock Distribution Agreement 10,576,180 shares of outstanding common stock were exchanged on a share-for-share basis for shares of non-voting common stock. In February 2013, all of the remaining outstanding shares of non-voting common stock were converted to voting shares in accordance with the Stock Distribution Agreement. As of December 31, 2014 and 2013, there were no shares of non-voting common stock outstanding.
	Preferred Stock
	The Company’s board of directors has the authority, without further action by the Company’s stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series and to fix the rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of such series, any or all of which may be greater than the rights of common stock. The Company’s issuance of preferred stock could adversely affect the voting power of holders of common stock and the likelihood that such holders will receive dividend payments and payments upon liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing a change of control of the Company or other corporate action. As of December 31, 2014 and 2013, there were no shares of preferred stock outstanding.

StockBased_Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-Based Compensation
	The Company has stock plans under which directors, officers, key employees and consultants of the Company may be granted restricted stock awards, stock options and other equity-based instruments as a means of promoting the Company’s long-term growth and profitability. The plans are intended to encourage participants to contribute to and participate in the success of the Company.
	The Company's board of directors adopted, and the Company's stockholders approved, the Amended and Restated 2005 Incentive Stock Plan, or the 2005 Stock Plan, effective January 1, 2008. The total number of shares of common stock authorized for issue pursuant to awards granted under the 2005 Stock Plan was 2,500,000 shares. The 2005 Stock Plan provided for the grant of non-qualified stock options, stock appreciation rights, restricted stock, performance shares, phantom stock, restricted stock units and other awards that are valued in whole or in part by reference to the Company's stock.
	On May 9, 2011, the Company's board of directors adopted, and the Company's stockholders approved, the 2011 Equity Incentive Award Plan, or 2011 Plan. Under the 2011 Plan, 3,000,000 new shares of common stock are reserved for issuance pursuant to a variety of stock-based compensation awards, including stock options, stock appreciation rights or SARs, restricted stock awards, restricted stock unit awards, deferred stock awards, dividend equivalent awards, stock payment awards and performance share awards and other stock-based awards, plus the number of shares remaining available for future awards under the Company's 2005 Stock Plan. The number of shares reserved for issuance or transfer pursuant to awards under the 2011 Plan will be increased by the number of shares represented by awards outstanding under the Company's 2005 Stock Plan that are forfeited or lapse unexercised and which, following the effective date of the 2011 Plan, are not issued under the Company's 2005 Stock Plan. No further awards will be granted under the 2005 Stock Plan, and all outstanding awards will continue to be governed by their existing terms. As of December 31, 2014 and December 31, 2013, 2,682,457 and 2,789,276 shares of the Company’s common stock, respectively, remained available for future issuance under the 2011 Plan.
	Stock-based compensation cost is included within salaries, wages and benefits in operating expenses in the accompanying statements of operations. Stock-based compensation cost amounted to $8.8 million, $5.7 million and $4.3 million for 2014, 2013 and 2012, respectively. During 2014, 2013 and 2012, there was $3.2 million, $2.1 million and $1.6 million tax benefit recognized in income related to stock-based compensation, respectively.
	Restricted Stock and Restricted Stock Units
	Restricted stock and restricted stock unit awards are valued at the fair value of the shares on the date of grant. Generally, granted shares and units vest 25% per year on each anniversary of issuance. Each restricted stock unit represents the right to receive one share of common stock upon vesting of such restricted stock unit. Vesting of restricted stock units is based on time-based service conditions. In order to vest, the participant must still be employed by the Company, with certain contractual exclusions, at each vesting event. Within 30 days after vesting, the shares underlying the award will be issued to the participant. In the event a successor corporation in a change in control situation fails to assume or substitute for the restricted stock units, the restricted stock units will automatically vest in full as of immediately prior to the consummation of such change in control. In the event of death or permanent disability of a participant, the restricted stock units will automatically vest in full. Compensation expense, net of forfeitures, is recognized on a straight-line basis over the requisite service period.
	A summary of the status of the Company’s restricted stock shares (restricted stock awards and restricted stock unit awards) as of December 31, 2014 and changes during the year ended December 31, 2014 is presented below:
		Number of Shares			Weighted-Average
					Grant Date Fair Value ($)
	Outstanding at December 31, 2013	336,048			22.99
	Granted	182,464			55.14
	Vested	(111,782	)		22.96
	Forfeited	(42,839	)		25.47
	Outstanding at December 31, 2014	363,891			38.83
	There were 182,464 and 151,202 restricted stock shares granted during the years ended December 31, 2014 and December 31, 2013, respectively. As of December 31, 2014 and December 31, 2013, there was $10.6 million and $6.1 million, respectively, of total unrecognized compensation cost related to nonvested restricted stock to be recognized over 2.8 years and 2.7 years, respectively.
	The weighted-average fair value of restricted stock granted during the years ended December 31, 2014, 2013 and 2012 was $55.14, $27.70 and $20.01, respectively. The total fair value of restricted stock shares vested during the years ended December 31, 2014, 2013 and 2012 was $6.5 million, $4.3 million and $3.9 million respectively.
	Stock Options
	Stock option awards are granted with an exercise price equal to the fair market value of the Company’s common stock at the date of grant, vest over four years of continuous service and have ten-year contractual terms. The fair value of each stock option award is estimated on the date of grant using the Black Scholes model. There were no options granted during 2014, 2013, or 2012. For option grants during 2011, the Company’s weighted average assumptions for expected volatility, dividends, term and risk-free interest rate were 46.25%, 0%, 6.25 years and 2.03%, respectively. Expected volatilities are based on the historical volatility of a group of peer entities within the same industry. The expected term of options is based upon the simplified method, which represents the average of the vesting term and the contractual term. The risk-free interest rate is based on U.S. Treasury yields for securities with terms approximating the expected term of the option.
	Prior to the Company's IPO, to the extent a market price was not available, the fair value of the Company’s common stock was estimated using a discounted cash flow analysis and market multiples, based on management’s estimates of revenue, driven by assumed market growth rates, and estimated costs as well as appropriate discount rates. These estimates are consistent with the plans and estimates management uses to manage the Company’s business.
	A summary of share option activity under the 2011 Plan as of December 31, 2014 and changes during the year ended December 31, 2014 is presented below:
		Number			Weighted-		Average	Aggregate
		of Options			Average		Remaining	Intrinsic
					Exercise		Contractual	Value
					Price ($)		Term	$0
							(Years)
	Outstanding at December 31, 2013	56,500			8.26		6.7	2,099
	Exercised	(21,125	)		8.18
	Forfeited or expired	(3,750	)		8.21
	Outstanding at December 31, 2014	31,625			8.32		5.7	2,127
	Exercisable at December 31, 2014	30,875			8.22		5.7	2,080
	Vested or Expected to Vest at December 31, 2014	31,614			8.32		5.7	2,126
	There were no options granted during the years ended December 31, 2014, 2013, or 2012. The total intrinsic value of share options exercised during the years ended December 31, 2014, 2013 and 2012 was $1.3 million, $2.0 million and $0.7 million, respectively. The total fair value of options vested during the years ended December 31, 2014, 2013 and 2012 was $0.1 million, $0.2 million and $0.4 million, respectively.
	As of December 31, 2014 and December 31, 2013, there was $3.1 thousand and $46.7 thousand respectively, of total unrecognized compensation cost related to options expected to be recognized over 0.7 years and 0.8 years, respectively.
	Performance Share Awards
	During 2014 and 2013, the Company granted certain senior-level executives performance stock units that vest based on market and time-based service conditions as part of a long-term incentive plan, which are referred to herein as performance share awards. The number of shares of common stock underlying each award is determined at the end of a three-year performance period. In order to vest, the senior level executive must still be employed by the Company, with certain contractual exclusions, at the end of the performance period. At the end of the performance period, the percentage of the stock units that will vest will be determined by ranking the Company’s total shareholder return compared to the total shareholder return of the peer companies identified in the plan. Based on the level of performance, between 0% and 200% of the award may vest. Within 60 days after vesting, the shares underlying the award will be issued to the participant. In the event of a change in control of the Company or the death or permanent disability of a participant, the payout of any award is limited to a pro-rated portion of such award based upon a performance assessment prior to the change-in-control date or date of death or permanent disability.
	The market condition requirements are reflected in the grant date fair value of the award, and the compensation expense, net of forfeitures, for the award will be recognized assuming that the requisite service is rendered regardless of whether the market conditions are achieved.
	The grant date fair value of the performance share awards was determined through the use of a Monte Carlo simulation model, which utilizes multiple input variables that determine the probability of satisfying the market condition requirements applicable to each award as follows:
		Weighted-Average at Grant Date for Twelve Months Ended December 31, 2014			Weighted-Average at Grant Date for Twelve Months Ended December 31, 2013
	Expected volatility factor	0.42			0.41
	Risk free interest rate	0.65		%	0.33	%
	Expected term (in years)	2.77			2.65
	Expected dividend yield	—		%	—	%
	For grants awarded in 2014, the volatility was based upon a weighted average historical volatility for the Company. For grants awarded in 2013 and 2012, the volatility was based upon a weighted average of the volatility for the Company and the most recent volatility of the peer group as there was not sufficient historical data for the Company alone. The peer group used to calculate volatility is consistent with the group used for the traditional employee stock options. The Company chose to use historical volatility to value these awards because historical prices were used to develop the correlation coefficients between the Company and each of the peer companies within the peer group in order to model stock price movements. The volatilities used were calculated as the remaining term of the performance period at the date of grant. The risk-free interest rate was based on the implied yield available on U.S. Treasury zero-coupon issues with remaining terms equivalent to the remaining performance period. The Company does not intend to pay dividends on its common stock in the foreseeable future. Accordingly, the Company used a dividend yield of zero in its model.
	The following table summarizes the Company’s performance share awards for the year ended December 31, 2014:
		Number of Awards			Weighted-Average Fair Value at Grant Date ($)
	Outstanding at December 31, 2013	327,104			22.94
	Granted	53,841			59.45
	Vested	(185,907	)		20.4
	Forfeited	(52,468	)		23.92
	Outstanding at December 31, 2014	142,570			39.67
	As of December 31, 2014 and December 31, 2013, there was $4.5 million and $6.5 million, respectively, of total unrecognized compensation cost related to performance share awards expected to be recognized over 1.64 years and 1.54 years, respectively.

Net_Income_per_Share

Net Income per Share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income per Share	Net Income per Share
	The following table sets forth the computation of basic and diluted earnings per common share:
		Year Ended December 31,
		2014		2013		2012
		(in thousands, except per share amounts)
	Numerator:
	Net income	$	225,464	$	176,918	$	108,460
	Denominator:
	Weighted-average shares outstanding, basic	72,739		72,593		72,386
	Effect of dilutive stock awards	555		406		205
	Adjusted weighted-average shares outstanding, diluted	73,294		72,999		72,591
	Net Income per Share:
	Basic earnings per common share	$	3.1	$	2.44	$	1.5
	Diluted earnings per common share	$	3.08	$	2.42	$	1.49
	Anti-dilutive weighted-average shares	29		1		88

Debt_and_Other_Obligations

Debt and Other Obligations	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Debt and Other Obligations	Debt and Other Obligations
	Long-term Debt
	On October 1, 2014, the Company entered into a Framework Agreement, with a bank syndicate which will provide up to $379 million of debt financing for seven Airbus A320 aircraft and three Airbus A321 aircraft. Each loan to be extended under the Framework Agreement will be funded on or about the delivery date of each aircraft and will be secured by a first-priority security interest in the individual aircraft. Each loan amortizes quarterly on a mortgage-style basis, with senior loans having a 12-year term and junior loans having a 7-year term. Loans will bear interest payable quarterly on a floating rate basis, provided that the Company may elect in advance a fixed rate basis. As of December 31, 2014, the Company has taken delivery of four Airbus A320 aircraft financed through the Framework Agreement and recorded debt of $148 million. The remaining three Airbus A320 aircraft and three Airbus A321 aircraft are scheduled for delivery under the Company's existing purchase agreement with Airbus between January 2015 and September 2015.
	Long-term debt is comprised of the following:
			As of December 31,
			2014			2013		2014		2013
			(in millions)					(weighted-average interest rates)
	Senior Term Loans due through 2026		$	132		$	—	4.26	%	N/A
	Junior Term Loans due through 2021		16			—		6.94	%	N/A
	Long-term debt		$	148		$	—
	Less current maturities		10.4			—
	Less unamortized discount, net		1.8			—
	Total		$	135.8		$	—
	During 2014, the Company did not make any debt payments and is set to begin repayment in January 2015.
	At December 31, 2014, long-term debt principal payments for the next five years and thereafter are as follows:
			December 31, 2014
			(in millions)
	2015		$	10.4
	2016		10.9
	2017		11.6
	2018		12
	2019		12.6
	2020 and thereafter		90.5
	Total debt principal payments		$	148
	Subsequent to December 31, 2014 and as of the date of this filing, the Company has taken delivery of two A320 aircraft resulting in $74.0 million of long-term debt.
	Interest Expense
	Interest expense related to debt consists of the following:
		Year Ended December 31,
		2014			2013
		(in thousands)
	Senior Term Loans	$	738		$	—
	Junior Term Loans	145			—
	Commitment fees	685			—
	Amortization of deferred financing costs	9			—
	Total	$	1,577		$	—
	The Company had unamortized deferred financing costs of $0.7 million as of December 31, 2014. As of December 31, 2013, the Company had no deferred financing costs. The long-term portion of these amounts is classified as other long-term assets on the balance sheet and is amortized over the term of the debt into interest expense.
	The Company's senior and junior term loans have an annual commitment fee, related to undisbursed loan amounts, of 0.75% and 1.25%, respectively, which is paid on a quarterly basis. As of December 31, 2014, the Company has incurred $0.2 million in commitment fees related to four Airbus A320 aircraft delivered in 2014 and $0.5 million in commitment fees for three Airbus A320 aircraft and three Airbus A321 aircraft scheduled for delivery in 2015. Commitment fee expense is included within interest expense on the statement of operations.
	As of December 31, 2014, the Company's capital leases are comprised of two quick engine change kits (QEC kit) and office equipment. Aggregate annual principal maturities of capital leases as of December 31, 2014 and December 31, 2013 are as follows:
			As of December 31,
			2014			2013
			(in thousands)
	2015		$	1,289		$	1,083
	2016		1,002			966
	2017		39			—
	2018		42			—
	2019		11			—
	2020 and thereafter		—			—
	Total principal maturities		$	2,383		$	2,049
	As of December 31, 2014 and 2013, the Company had a line of credit for $18.6 million related to corporate credit cards. Respectively, the Company had drawn $4.5 million and $3.7 million as of December 31, 2014 and 2013, which is included in accounts payable.
	As of December 31, 2014, the Company had lines of credit with counterparties for fuel derivatives and physical fuel delivery in the amount of $38.0 million. As of December 31, 2014, the Company had drawn $9.3 million on these lines of credit, which is included in other current liabilities. As of December 31, 2013, the Company had lines of credit with counterparties for both physical fuel delivery and fuel derivatives in the amount $34.5 million. As of December 31, 2013, the Company had drawn $13.8 million on these lines of credit, which is included in other current liabilities. The Company is required to post collateral for any excess above the lines of credit if the fuel derivatives are in a net liability position and make periodic payments in order to maintain an adequate undrawn portion for physical fuel delivery. As of December 31, 2014 and 2013, the Company did not hold any fuel derivatives with requirements to post collateral.

Leases_and_Prepaid_Maintenance

Leases and Prepaid Maintenance Deposits	12 Months Ended
	Dec. 31, 2014
Leases [Abstract]
Leases and Prepaid Maintenance Deposits	Leases and Prepaid Maintenance Deposits
	The Company leases various types of equipment and property, primarily aircraft, spare engines and airport facilities under leases, which expire in various years through 2032. Lease terms are generally 3 to 15 years for aircraft and up to 25 years for other leased equipment and property.
	Total rental expense for all leases charged to operations for the years ended 2014, 2013 and 2012 was $254.3 million, $214.6 million and $178.4 million, respectively. Total rental expense charged to operations for aircraft and engine operating leases for the years ended December 31, 2014, 2013 and 2012 was $195.8 million, $169.7 million and $143.6 million, respectively. Supplemental rent is made up of maintenance reserves paid or to be paid to aircraft lessors in advance of the performance of major maintenance activities that are not probable of being reimbursed and probable return condition obligations. The Company expensed $7.5 million, $5.2 million and $2.0 million of supplemental rent recorded within aircraft rent during 2014, 2013 and 2012, respectively.
	Some of the Company’s master lease agreements provide that the Company pays maintenance reserves to aircraft lessors to be held as collateral in advance of the Company’s required performance of major maintenance activities. Some maintenance reserve payments are fixed contractual amounts, while others are based on actual flight hours. Fixed maintenance reserve payments for these aircraft and related flight equipment, including estimated amounts for contractual price escalations, will be approximately $7.6 million in 2015, $8.0 million in 2016, $7.4 million in 2017, $5.8 million in 2018, $4.2 million in 2019 and $14.1 million in 2020 and beyond. These lease agreements provide that maintenance reserves are reimbursable to the Company upon completion of the maintenance event in an amount equal to either (1) the amount of the maintenance reserve held by the lessor associated with the specific maintenance event or (2) the qualifying costs related to the specific maintenance event. Substantially all of these maintenance reserve payments are calculated based on a utilization measure, such as flight hours or cycles, and are used solely to collateralize the lessor for maintenance time run off the aircraft until the completion of the maintenance of the aircraft. Some of the master lease agreements do not require that the Company pay maintenance reserves so long as the Company's cash balance does not fall below a certain level. The Company is in full compliance with those requirements and does not anticipate having to pay reserves related to these master leases in the future.
	At lease inception and at each balance sheet date, the Company assesses whether the maintenance reserve payments required by the master lease agreements are substantively and contractually related to the maintenance of the leased asset. Maintenance reserve payments that are substantively and contractually related to the maintenance of the leased asset are accounted for as maintenance deposits to the extent they are expected to be recoverable and are reflected as prepaid maintenance deposits in the accompanying balance sheets. When it is not probable the Company will recover amounts currently on deposit with a lessor, such amounts are expensed as supplemental rent. As of December 31, 2014 and 2013, the Company had aircraft maintenance deposits of $250.0 million and $220.7 million, respectively, on its balance sheets of which $36.9 million and $59.2 million, respectively, are included within prepaid expenses and other current assets on its balance sheets. The Company has concluded that these prepaid maintenance deposits are probable of recovery primarily due to the rate differential between the maintenance reserve payments and the expected cost for the related next maintenance event that the reserves serve to collateralize.
	The Company’s master lease agreements also provide that most maintenance reserves held by the lessor at the expiration of the lease are nonrefundable to the Company and will be retained by the lessor. Consequently, any usage-based maintenance reserve payments after the last major maintenance event are not substantively related to the maintenance of the leased asset and therefore are accounted for as contingent rent. The Company accrues for contingent rent beginning when it becomes probable and reasonably estimable the Company will incur such nonrefundable maintenance reserve payments. The Company makes certain assumptions at the inception of the lease and at each balance sheet date to determine the recoverability of maintenance deposits. These assumptions are based on various factors such as the estimated time between the maintenance events, the date the aircraft is due to be returned to the lessor, and the number of flight hours the aircraft is estimated to be utilized before it is returned to the lessor. The Company expensed $1.6 million, $1.9 million and $2.0 million of paid maintenance reserves as supplemental rent during 2014, 2013 and 2012, respectively. Maintenance reserves held by lessors that are refundable to the Company at the expiration of the lease are accounted for as prepaid maintenance deposits on the balance sheet when they are paid.
	At December 31, 2014, the Company had 61 aircraft and 10 spare engines financed under operating leases with lease term expiration dates ranging from 2016 to 2026. Five of the leased aircraft have variable rent payments, which fluctuate based on changes in LIBOR (London Interbank Offered Rate). The Company has the option to renew three leases for three-year periods with contractual notice required in the tenth year. Thirty-one of the aircraft leases and all of the engine leases were the result of sale and leaseback transactions. Deferred gains or losses from sale and leaseback transactions are amortized over the term of the lease as a reduction in rent or additional rent, respectively. Losses are deferred when the fair value of the aircraft or engine is higher than the price it was sold for, which is in substance, a prepayment of rent. A loss on disposal is recorded at the time of sale for the excess of the carrying amount over the fair value of the aircraft or engine.
	During 2014, the Company entered into sale and leaseback transactions with third-party aircraft lessors for the sale and leaseback of eight Airbus A320 aircraft that resulted in net deferred losses of $1.6 million, which are included in other long-term assets on the accompanying balance sheet. Deferred losses are recognized as an increase to rent expense on a straight-line basis over the term of the respective operating leases. Deferred gains are included in deferred gains and other long-term liabilities on the accompanying balance sheet. Deferred gains are recognized as a decrease to rent expense on a straight-line basis over the term of the respective operating leases. The Company had agreements in place prior to the delivery of these aircraft which resulted in the settlement of the purchase obligation by the lessor and the refund of $53.2 million in pre-delivery deposits from Airbus during 2014. The refunded pre-delivery deposits have been disclosed in the statement of cash flows as investing activities within pre-delivery deposits, net of refunds. In addition, the Company entered into a sale and leaseback transaction with a third-party lessor for the sale and leaseback of one V2500 IAE International Aero Engines AG engine. Cash outflows related to the purchase of the engine have been disclosed in the statement of cash flows as investing activities within purchases of property and equipment and the cash inflows from the sale of the engine as financing activities within proceeds received on sale lease back transactions. All of the leases from these sale and leaseback transactions are accounted for as operating leases. Under the terms of the lease agreements, the Company will continue to operate and maintain the aircraft. Payments under the lease agreements are fixed for the term of the lease. The lease agreements contain standard termination events, including termination upon a breach of the Company's obligations to make rental payments and upon any other material breach of the Company's obligations under the leases, and standard maintenance and return condition provisions. Upon a termination of the lease due to a breach by the Company, the Company would be liable for standard contractual damages, possibly including damages suffered by the lessor in connection with remarketing the aircraft or while the aircraft is not leased to another party. The Company has an agreement for the lease of two QEC kits, classified as capital leases. Payments under the lease agreement are fixed for the three year term of the lease.
	The Company had two QEC kits classified as capital leases at December 31, 2014 and 2013. Amortization of assets recorded under capital leases are included within depreciation expense. Amounts applicable to these QEC kits that are included in property and equipment were:
		2014		2013
		(in thousands)
	Flight equipment	$	3,234	$	3,234
	Less: accumulated amortization	377		54
		$	2,857	$	3,180
	Future minimum lease payments under capital leases and noncancellable operating leases with initial or remaining terms in excess of one year at December 31, 2014 were as follows:
				Operating Leases
		Capital Leases		Aircraft and Spare Engine Leases		Property Facility Leases		Total Operating Leases
		(in thousands)
	2015	$	1,444	$	214,337	$	29,647	$	243,984
	2016	1,044		212,512		25,239		237,751
	2017	44		196,010		25,613		221,623
	2018	44		172,323		25,759		198,082
	2019	12		144,211		23,606		167,817
	2020 and thereafter	—		592,409		71,578		663,987
	Total minimum lease payments	$	2,588	$	1,531,802	$	201,442	$	1,733,244
	Less amount representing interest	205
	Present value of minimum lease payments	2,383
	Less current portion	1,289
	Long-term portion	1,094

Financial_Instruments_and_Risk

Financial Instruments and Risk Management	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Financial Instruments and Risk Management	Financial Instruments and Risk Management
	As part of the Company’s risk management program, the Company from time to time uses a variety of financial instruments to reduce its exposure to fluctuations in the price of jet fuel and interest rates. The Company does not hold or issue derivative financial instruments for trading purposes.
	The Company is exposed to credit losses in the event of nonperformance by counterparties to these financial instruments. The Company periodically reviews and seeks to mitigate exposure to the financial deterioration and nonperformance of any counterparty by monitoring the absolute exposure levels, each counterparty's credit ratings and the historical performance of the counterparties relating to hedge transactions. The credit exposure related to these financial instruments is limited to the fair value of contracts in a net receivable position at the reporting date. The Company also maintains security agreements that require the Company to post collateral if the value of selected instruments falls below specified mark-to-market thresholds. As of December 31, 2014, the Company did not hold any derivatives with requirements to post collateral. The Company records financial derivative instruments at fair value, which includes an evaluation of each counterparty's credit risk.
	Fuel Derivative Instruments
	The Company's fuel derivative contracts generally consist of United States Gulf Coast jet fuel swaps (jet fuel swaps) and United States Gulf Coast jet fuel options (jet fuel options). Both jet fuel swaps and jet fuel options are used at times to protect the refining price risk between the price of crude oil and the price of refined jet fuel, and to manage the risk of increasing fuel prices. Fair value of the instruments is determined using standard option valuation models.
	The Company accounts for its fuel derivative contracts at fair value and recognizes them in the balance sheet in prepaid expenses and other current assets or other current liabilities. The Company did not elect hedge accounting on any fuel derivative instruments entered into during 2014, 2013 and 2012 and, as a result, changes in the fair value of these fuel derivative contracts are recorded in aircraft fuel expense. During 2014, the Company paid $9.7 million in premiums to acquire fuel options.
	The following table summarizes the components of aircraft fuel expense for the years ended December 31, 2014, 2013 and 2012:
		Year Ended December 31,
		2014		2013		2012
		(in thousands)
	Into-plane fuel cost	$	608,033	$	542,523	$	471,542
	Realized losses (gains)	995		8,958		175
	Unrealized mark-to-market losses (gains)	3,881		265		46
	Aircraft fuel	$	612,909	$	551,746	$	471,763
	Premiums and settlements received or paid on fuel derivative contracts are reflected in the accompanying statements of cash flows in net cash provided by operating activities.
	During the third quarter of 2014, the Company became aware of an underpayment of Federal Excise Tax (FET) for fuel purchases during the period between July 1, 2009 and August 31, 2014. The commencement of the period in which the Company underpaid FET coincided with a change in its fuel service provider that took place in July 2009. The amount of underpayment of jet fuel FET from July 1, 2009 through December 31, 2013 is $9.3 million along with an additional $2.1 million for the year ended December 31, 2014. Approximately, $0.8 million of interest was incurred related to the past-due tax payments. The Company does not believe the error to be material to the 2009 through 2013 financial statements nor for the cumulative out of period error to be material to the current year financial statements.
	As of December 31, 2014, the Company had fuel derivatives consisting of jet fuel options with refined products as the underlying commodities designed to protect 88.7 million gallons, or approximately 35% of its 2015 anticipated jet fuel consumption, at a weighted-average ceiling price of $2.07. As of December 31, 2013, the Company had no outstanding fuel derivatives in place.
	Interest Rate Swaps
	On October 23, 2014, the Company entered into six forward interest rate swaps, with a total notional amount of $120 million. The interest rate swaps fix the benchmark interest rate component of the forecasted interest payments on the debt related to three Airbus A321 aircraft with expected delivery dates ranging from July 2015 to September 2015. These instruments limit the Company's exposure to changes in the benchmark interest rate in the period from the trade date through the date of maturity, ranging from July 2015 to September 2015. The interest rate swaps are designated as cash flow hedges. The Company accounts for these interest rate swaps at fair value and recognizes them in the balance sheet in prepaid expenses and other current assets or other current liabilities with changes in fair value recorded within accumulated other comprehensive income (AOCI). Realized gains and losses from cash flow hedges are recorded in the statement of cash flows as a component of cash flows from operating activities. For the twelve months ended December 31, 2014, a loss of $0.7 million, net of deferred taxes of $0.4 million, was recorded within AOCI related to these instruments. As of December 31, 2014, the interest rate swaps are recorded as a liability of approximately $1.1 million.
	In 2014, the Company recorded no ineffectiveness associated with the Company's interest rate cash flow hedges. The Company expects the swaps will be highly effective in offsetting changes in cash flows attributable to the hedged risk. However, given that there may be some uncertainty regarding the exact date on which the Company will issue its fixed-rate debt, the Company will evaluate the effect of such uncertainty on the effectiveness of the hedging relationship designated hereunder each reporting period. Any ineffectiveness will be recorded within other non-operating expense in the Company's statement of operations.
	Subsequent to the issuance of each debt instrument, amounts remaining in AOCI will be amortized over the life of the fixed-rate debt instrument.

Defined_Contribution_401k_Plan

Defined Contribution 401(k) Plan	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Defined Contribution 401(k) Plan	Defined Contribution 401(k) Plan
	The Company sponsors three defined contribution 401(k) plans, Spirit Airlines, Inc. Employee Retirement Savings Plan (first plan), Spirit Airlines, Inc. Pilots’ Retirement Savings Plan (second plan) and Spirit Airlines, Inc. Puerto Rico Retirement Savings Plan (third plan). The first plan was adopted on February 1, 1994. Essentially, all employees that are not covered by the pilots’ collective bargaining agreement, who have at least 1 year of service, have worked at least 1,000 hours during the year and have attained the age of 21 may participate in this plan. The Company may make a Qualified Discretionary Contribution, as defined in the plan, or provide matching contributions to this plan. Effective July 1, 2007, the Company amended this plan to change the service requirement to 60 days and provided for matching contribution to the plan at 50% of the employee’s contribution up to a maximum employer contribution of 3% of the employee’s annual compensation.
	The second plan is for the Company’s pilots, and contained the same service requirements as the first plan and was amended effective July 1, 2007, to change the service requirements to 60 days and having attained the age of 21. Throughout the majority of 2014, the Company matched 100% of the pilot’s contribution, up to 8% of the individual pilot’s annual compensation. Effective August 1, 2014, the Company matches 100% of the pilot's contribution, up to 9% of the individual pilot's annual compensation. Both the first and the second plans are subject to the annual IRS elective deferral limit, which was $17,500 for 2014.
	The third plan is for all Company employees residing in Puerto Rico and was adopted on April 16, 2012. It contains the same amended service requirements as the first and second plans. For pilots participating in the Puerto Rico plan, the Company matches 100% of their contribution, up to 9% of the individual pilot's annual compensation, but subject to the annual Puerto Rico pre-tax elective deferral limit, which was $17,500 for 2014. Prior to August 1, 2014, the Company matched 100% of the pilot's contribution, up to 8% of the individual pilot's annual compensation. For all other employees participating in the Puerto Rico plan, the Company provides for matching contribution to the plan at 50% of the employee's contribution up to a maximum employer contribution of 3% of the employee's annual compensation.
	Matching contributions made to all plans were $9.7 million, $7.7 million and $6.6 million in 2014, 2013 and 2012, respectively, and were included within salaries, wages and benefits in the accompanying statements of operations.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	Significant components of the provision for income taxes from continuing operations are as follows:
		Year Ended December 31,
		2014				2013				2012
		(in thousands)
	Current:
	Federal	$	85,966			$	86,437			$	32,656
	State and local	5,389				6,595				3,250
	Foreign	2,057				413				963
	Total current expense	93,412				93,445				36,869
	Deferred:
	Federal	34,240				11,658				27,870
	State and local	(122		)		389				1,385
	Total deferred expense (benefit)	34,118				12,047				29,255
	Total income tax expense (benefit)	$	127,530			$	105,492			$	66,124
	The income tax provision differs from that computed at the federal statutory corporate tax rate as follows:
		Year Ended December 31,
		2014			2013			2012
	Expected provision at federal statutory tax rate	35	%		35	%		35	%
	State tax expense, net of federal benefit	1	%		1.7	%		2.1	%
	Income tax credits	(0.4	)%		—	%		(0.1	)%
	Other	0.5	%		0.7	%		0.9	%
	Total income tax expense (benefit)	36.1	%		37.4	%		37.9	%
	The Company accounts for income taxes using the asset and liability method. Deferred taxes are recorded based on differences between the financial statement basis and tax basis of assets and liabilities and available tax loss and credit carryforwards. At December 31, 2014 and 2013, the significant components of the Company's deferred taxes consisted of the following:
		December 31,
		2014				2013
		(in thousands)
	Deferred tax assets:
	Net operating loss	$	252			$	188
	Accrued rent	—				1,872
	Deferred revenue	410				6,241
	Nondeductible accruals	12,239				6,702
	Deferred manufacturing credits	848				3,309
	Unrealized gains/losses on derivatives	1,865				—
	Accrued maintenance	3,073				1,225
	Equity compensation	4,514				2,687
	Other	661				16
	Deferred tax assets	23,862				22,240
	Deferred tax liabilities:
	Capitalized interest	568				736
	Deferred gain and losses on leases, net	2,349				1,882
	Accrued rent	2,560				—
	Prepaid expenses	1,681				—
	Property, plant and equipment	37,369				6,384
	Accrued engine maintenance	45,702				45,911
	Deferred tax liabilities	90,229				54,913
	Net deferred tax assets (liabilities)	$	(66,367	)		$	(32,673	)
	Deferred taxes included within:
	Assets:
	Current deferred tax assets, net	$	9,643			$	16,243
	Liabilities:
	Noncurrent deferred tax liabilities, net	$	76,010			$	48,916
	In assessing the realizability of the deferred tax assets, management considered whether it is more likely than not that some or all of the deferred tax assets would be realized. In evaluating the Company’s ability to utilize its deferred tax assets, it considered all available evidence, both positive and negative, in determining future taxable income on a jurisdiction by jurisdiction basis. Management does not believe that the realization of deferred tax assets is in jeopardy and thus a valuation allowance for 2014 will not be necessary.
	The Company has fully utilized its federal NOL carryforwards and AMT credit carryforwards as of December 31, 2012. At December 31, 2014, the Company has state net operating loss carryforwards of approximately $2.7 million which can be used to offset future state taxable income. State net operating losses begin to expire in 2017.
	Excess tax benefits are only recognized in the financial statements upon actual realization of the related tax benefit which occurred in 2012 upon utilization of the remaining NOLs and AMT credit carryforwards during the year. During 2014, the Company recognized a windfall tax benefit of $1.9 million which was recorded as a reduction to income tax payable and a corresponding entry to additional paid in capital.
	The Company recorded a current foreign tax credit of $1.2 million against its 2014 federal income tax liability which was fully utilized during the year. During 2014, the Company amended its 2005 through 2012 U.S. federal income tax returns to credit foreign taxes of $1.4 million against U.S. income taxes previously paid.
	The Company filed an advance consent change in tax accounting method for its lease payments on certain leased aircraft, effective for its 2014 tax year. The estimated tax impact of this tax accounting method change reduces income tax payable in the amount of $35 million, with a corresponding increase in noncurrent deferred tax liability. The Company has yet to receive advance consent for this tax accounting method change and, therefore, has not included the tax impact in the balance sheet as of December 31, 2014.
	On September 13, 2013, the United States Treasury and Internal Revenue Service issued final tangible personal property regulations that broadly apply to amounts paid to acquire, produce or improve tangible property, as well as dispositions of such property. In review of these regulations, the Company has concluded that there is no material impact on its financial position, results of operations or cash flows.
	The Company's policy is to recognize interest and penalties accrued on any unrecognized tax benefits as a component of selling, general and administrative expenses. For tax years ended December 31, 2014, 2013 and 2012, the Company did not recognize any liabilities for uncertain tax positions nor any interest and penalties on unrecognized tax benefits.
	The Company files its tax returns as prescribed by the tax laws of the jurisdictions in which it operates. The Company's tax years from 2006 through 2013 are still subject to examination for federal income tax purposes, due to net operating loss carryovers generated in such years. Various state and foreign jurisdiction tax years remain open to examination. The Company is currently under audit with various state jurisdictions. The Company believes that any potential assessment would be immaterial to its financial statements.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies
	Aircraft-Related Commitments and Financing Arrangements
	The Company’s contractual purchase commitments consist primarily of aircraft and engine acquisitions through manufacturers and aircraft leasing companies. As of December 31, 2014, the Company's aircraft orders consisted of the following:
		Airbus				Third-Party Lessor
		A320	A320NEO	A321	A321NEO	A320NEO	Total
	2015	8		6		1	15
	2016	3		9		4	16
	2017	8		10			18
	2018	2	6	5			13
	2019		3		10		13
	2020		13				13
	2021		18				18
		21	40	30	10	5	106
	The Company also has five spare engine orders for V2500 SelectOne engines with IAE and nine spare engine orders for PurePower PW 1100G-JM engines with Pratt & Whitney. Spare engines are scheduled for delivery from 2015 through 2024. Purchase commitments for these aircraft and engines, including estimated amounts for contractual price escalations and pre-delivery payments, will be approximately $660.1 million in 2015, $604.0 million in 2016, $763.4 million in 2017, $621.4 million in 2018, $711.1 million in 2019 and $1,525.3 million in 2020 and beyond. The Company has secured financing commitments with third parties for six aircraft deliveries from Airbus, scheduled for delivery in 2015 and for the five aircraft to be leased directly from a third party. The Company does not have financing commitments in place for the remaining 95 Airbus firm aircraft orders scheduled for delivery between 2015 and 2021. However, the Company has signed letters of intent to finance five of these aircraft being delivered in 2015 under secured debt arrangements.
	The Company is contractually obligated to pay the following minimum guaranteed payments for its reservation system and advertising media as of December 31, 2014: $5.1 million in 2015, $3.9 million in 2016, $3.9 million in 2017, $2.6 million in 2018, $0.0 million in 2019 and $0.0 million in 2020 and thereafter.
	Litigation
	The Company is subject to commercial litigation claims and to administrative and regulatory proceedings and reviews that may be asserted or maintained from time to time. The Company believes the ultimate outcome of such lawsuits, proceedings and reviews will not, individually or in the aggregate, have a material adverse effect on its financial position, liquidity or results of operations.
	Employees
	The Company has four union-represented employee groups that together represent approximately 67% of all employees at December 31, 2014. The Company had three union-represented employee groups that together represented approximately 59% of all employees at December 31, 2013. The table below sets forth the Company's employee groups and status of the collective bargaining agreements as of December 31, 2014.
	Employee Groups	Representative	Amendable Date	Percentage of Workforce
	Pilots	Air Line Pilots Association, International (ALPA)	August 2015	25%
	Flight Attendants	Association of Flight Attendants (AFA-CWA)	Aug-07	35%
	Dispatchers	Transport Workers Union (TWU)	Aug-18	1%
	Ramp Service Agents	International Association of Machinists and Aerospace Workers (IAM)	TBD	6%
	In August 2014, under the supervision of the National Mediation Board (NMB), the Company and AFA-CWA reached a tentative agreement for a five-year contract with the Company's flight attendants. The tentative agreement was subject to ratification by the flight attendant membership. On October 1, 2014, the Company was notified that the flight attendants voted not to ratify the tentative agreement. The Company will continue to work together with the AFA-CWA and the NMB with a goal of reaching a mutually beneficial agreement. On July 8, 2014, approximately 250 ramp service agents directly employed by the Company voted to be represented by the International Association of Machinists and Aerospace Workers (IAM). As of December 31, 2014, these ramp service agents served 4 of the 56 airports where the Company operates. The Company has begun the process of negotiating a collective bargaining agreement with the IAM.
	The Company is self-insured for health care claims, subject to a stop-loss policy, for eligible participating employees and qualified dependent medical claims, subject to deductibles and limitations. The Company’s liabilities for claims incurred but not reported are determined based on an estimate of the ultimate aggregate liability for claims incurred. The estimate is calculated from actual claim rates and adjusted periodically as necessary. The Company has accrued $3.1 million and $2.1 million, for health care claims as of December 31, 2014, and 2013, respectively.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements
	Under ASC 820, Fair Value Measurements and Disclosures, disclosures are required about how fair value is determined for assets and liabilities, and a hierarchy for which these assets and liabilities must be grouped is established, based on significant levels of inputs, as follows:
	Level 1—Quoted prices in active markets for identical assets or liabilities.
	Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.
	Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
	Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The Company utilizes several valuation techniques in order to assess the fair value of the Company’s financial assets and liabilities.
	Fuel Derivative Instruments
	The Company’s fuel derivative contracts generally consist of jet fuel swaps and jet fuel options. These instruments are valued using energy and commodity market data, which is derived by combining raw inputs with quantitative models and processes to generate forward curves and volatilities.
	The Company utilizes the market approach to measure fair value for its fuel derivative instruments. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities.
	The Company did not elect hedge accounting on any of the fuel derivative instruments. As a result, the Company records the fair value adjustment of its fuel derivatives in the accompanying statement of operations within aircraft fuel and on the balance sheet within prepaid expenses and other current assets or other current liabilities, depending on whether the net fair value of the derivatives is on an asset or liability position as of the respective date. Fair values of the fuel derivative instruments are determined using standard option valuation models. The Company also considers counterparty risk and its own credit risk in its determination of all estimated fair values. The Company offsets fair value amounts recognized for derivative instruments executed with the same counterparty under a master netting arrangement. The Company determines fair value of jet fuel options utilizing an option pricing model based on inputs that are either readily available in public markets or can be derived from information available in publicly quoted markets. The Company has consistently applied these valuation techniques in all periods presented and believes it has obtained the most accurate information available for the types of derivative contracts it holds.
	The fair value of the Company's jet fuel swaps are 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 categorizes these instruments as Level 2. As of December 31, 2014 and 2013, the Company had no outstanding jet fuel swaps. Due to the fact that certain inputs utilized to determine the fair value of jet fuel options are unobservable (principally implied volatility), the Company categorizes these derivatives as Level 3. Implied volatility of a jet fuel option is the volatility of the price of the underlying commodity that is implied by the market price of the option based on an option pricing model. Thus, it is the volatility that when used in a particular pricing model, yields a theoretical value for the option equal to the current market price of that option. Implied volatility, a forward-looking measure, differs from historical volatility because the latter is calculated from known past returns. At each balance sheet date, the Company substantiates and adjusts unobservable inputs. The Company routinely assesses the valuation model's sensitivity to changes in implied volatility. Based on the Company's assessment of the valuation model's sensitivity to changes in implied volatility, it noted that holding other inputs constant, a significant increase (decrease) in implied volatility would result in significantly higher (lower) determination of fair value measurement for the Company's aircraft fuel derivatives.
	Interest Rate Swaps
	The fair value of the Company's interest rate swaps are based on observable inputs for active swap indications in quoted markets for similar terms. The fair value of these instruments are determined using a market approach based on inputs that are readily available from public markets; therefore, the Company categorizes these instruments as Level 2. The interest rate swaps are designated as cash flow hedges and, as a result, the changes in fair value of these derivatives are recorded in accumulated other comprehensive income within the balance sheet and statement of other comprehensive income.
	Long-Term Debt
	The estimated fair value of the Company's non publicly held debt agreements has been determined to be Level 3, as certain inputs used to determine the fair value of these agreements are unobservable. The Company utilizes a discounted cash flow method to estimate the fair value of the Level 3 long-term debt.
	The carrying amounts and estimated fair values of our long-term debt at December 31, 2014 were as follows:
		Carrying value			Estimated fair value
		(in millions)
	Senior long-term debt	$	132		$	132
	Junior long-term debt	16			16.1
	Total long-term debt	$	148		$	148.1
	Cash and Cash Equivalents
	Cash and cash equivalents at December 31, 2014 and December 31, 2013 are comprised of liquid money market funds and cash and are categorized as Level 1 instruments. The Company maintains cash with various high-quality financial institutions.
	Assets and liabilities measured at gross fair value on a recurring basis are summarized below:
		Fair Value Measurements as of December 31, 2014
		Total			Level		Level		Level
					1		2		3
		(in millions)
	Cash and cash equivalents	$	632.8		$	632.8	$	—	$	—
	Jet fuel options	4.8			—		—		4.8
	Total assets	$	637.6		$	632.8	$	—	$	4.8
	Interest rate swaps	$	1.1		$	—	$	1.1	$	—
	Total liabilities	$	1.1		$	—	$	1.1	$	—
		Fair Value Measurements as of December 31, 2013
		Total			Level		Level		Level
					1		2		3
		(in millions)
	Cash and cash equivalents	$	530.6		$	530.6	$	—	$	—
	Total assets	$	530.6		$	530.6	$	—	$	—
	Total liabilities	$	—		$	—	$	—	$	—
	The Company had no transfers of assets or liabilities between any of the above levels during the years ended December 31, 2014 and 2013.
	The Company's Valuation Group is made up of individuals from the Company's Treasury and Corporate Accounting departments. The Valuation Group is responsible for the Company's valuation policies, procedures and execution thereof. The Company's Valuation Group reports to the Company's Chief Financial Officer and seeks approval for certain derivative transactions from the Audit Committee. The Valuation Group compares the results of the Company's internally developed valuation methods with counterparty reports at each balance sheet date and assesses the Company's valuation methods for accurateness and identifies any needs for modification.
	The following table presents the Company’s activity for assets and liabilities measured at gross fair value on a recurring basis using significant unobservable inputs (Level 3):
		Jet Fuel Options
		(in millions)
	Balance at January 1, 2012	$	0.3
	Total realized or unrealized gains (losses) included in earnings, net	(0.2		)
	Purchases	—
	Sales	—
	Settlements, net	0.2
	Balance at December 31, 2012	0.3
	Total realized or unrealized gains (losses) included in earnings, net	0.1
	Purchases	—
	Sales	—
	Settlements, net	(0.4		)
	Balance at December 31, 2013	—
	Total realized or unrealized gains (losses) included in earnings, net	(4.9		)
	Purchases	9.7
	Sales	—
	Settlements, net	—
	Balance at December 31, 2014	$	4.8

Operating_Segments_and_Related

Operating Segments and Related Disclosures	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Operating Segments and Related Disclosures	Operating Segments and Related Disclosures
	The Company is managed as a single business unit that provides air transportation for passengers. Operating revenues by geographic region as defined by the Department of Transportation (DOT) area are summarized below:
		2014		2013		2012
		(in millions)
	DOT—domestic	$	1,728.80	$	1,467.50	$	1,135.10
	DOT—Latin America	202.8		186.9		183.3
	Total	$	1,931.60	$	1,654.40	$	1,318.40
	During 2014, 2013 and 2012, no revenue from any one foreign country represented greater than 4% of the Company’s total passenger revenue. The Company attributes operating revenues by geographic region based upon the origin and destination of each passenger flight segment. The Company’s tangible assets consist primarily of flight equipment, which are mobile across geographic markets and, therefore, have not been allocated.

Tax_Receivable_Agreement

Tax Receivable Agreement	12 Months Ended
	Dec. 31, 2014
Tax Receivable Agreement [Abstract]
Tax Receivable Agreement	Tax Receivable Agreement
	On June 1, 2011, the Company completed its initial public offering of common stock, or IPO. In connection with the IPO, the Company entered into the TRA and thereby distributed immediately prior to the completion of the IPO to the holders of common stock as of such time, or the Pre-IPO Stockholders, the right to receive an amount equal to 90% of the cash savings in federal income tax realized by it by virtue of the use of the federal net operating loss, deferred interest deductions and alternative minimum tax credits held by the Company as of March 31, 2011, which was defined as the Pre-IPO NOL. Cash tax savings were generally computed by comparing actual federal income tax liability to the amount of such taxes that the Company would have been required to pay had such Pre-IPO NOLs (as defined in the TRA) not been available. Upon consummation of the IPO and execution of the TRA, the Company recorded a liability with an offsetting reduction to additional paid in capital. The amount and timing of payments under the TRA depended upon a number of factors, including, but not limited to, the amount and timing of taxable income generated in future periods and any limitations that may have been imposed on the Company's ability to use the Pre-IPO NOLs. The term of the TRA was to continue until the first to occur (a) the full payment of all amounts required under the agreement with respect to utilization or expiration of all of the Pre-IPO NOLs, (b) the end of the taxable year including the tenth anniversary of the IPO or (c) a change in control of the Company.
	In accordance with the TRA, the Company was required to submit a Tax Benefit Schedule showing the proposed TRA payout amount to the Stockholder Representatives within 45 calendar days of the Company filing its tax return. Stockholder Representatives were defined as Indigo Pacific Partners, LLC and OCM FIE, LLC, representing the two largest ownership interest of pre-IPO shares. The Tax Benefit Schedule was to become final and binding on all parties unless a Stockholder Representative, within 45 calendar days after receiving such schedule, provided the Company with notice of a material objection to such schedule. If the parties, for any reason, were unable to successfully resolve the issues raised in any notice within 30 calendar days of receipt of such notice, the Company and the Stockholder Representatives had the right to employ the TRA's reconciliation procedures. If the Tax Benefit Schedule was accepted, the Company had five days after acceptance to make payments to the Pre-IPO stockholders. Pursuant to the TRA's reconciliation procedures, any disputes that could not be settled amicably, were to be settled by arbitration conducted by a single arbitrator jointly selected by both parties.
	During the second quarter of 2012, the Company paid $27.2 million, or 90% of the 2011 tax savings realized from the utilization of NOLs, including $0.3 million of applicable interest, to the Pre-IPO Stockholders.
	During 2013, the Company filed an amended 2009 income tax return which resulted in a reduction to the estimated TRA liability from $8.0 million to $5.6 million. On September 13, 2013, the Company filed its 2012 federal income tax return, and on October 14, 2013, the Company submitted the Tax Benefit Schedule to the Stockholder Representatives. On November 27, 2013, pursuant to the TRA, the Company received an objection notice to the Tax Benefit Schedule from the Stockholder Representatives. On April 7, 2014, the Company received a demand for arbitration from the Stockholder Representatives. Prior to commencing arbitration proceedings, on June 17, 2014, the Company and Stockholder Representatives agreed on a settlement amount of $7.0 million in addition to interest of $0.3 million. The agreed upon settlement was in excess of the outstanding liability of $5.6 million at the time of settlement. The excess payment of $1.4 million was recorded within other expense in the statement of operations and in the statement of cash flows as a component of cash flows from operating activities. As of December 31, 2014, the Company had made all payments in accordance with the agreed upon settlement terms and had no outstanding obligations related to the TRA.

Quarterly_Financial_Data_Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (Unaudited)	Quarterly Financial Data (Unaudited)
	Quarterly results of operations for the years ended December 31, 2014 and 2013 are summarized below:
		Three Months Ended
		31-Mar		30-Jun		30-Sep		31-Dec
		(in thousands, except per share amounts)
	2014
	Operating revenue	$	437,987	$	499,337	$	519,769	$	474,487
	Operating income	59,953		105,144		100,191		89,975
	Net income	37,706		64,849		67,000		55,909
	Basic earnings per share	0.52		0.89		0.92		0.77
	Diluted earnings per share	0.51		0.88		0.91		0.76
	2013
	Operating revenue	$	370,437	$	407,339	$	456,625	$	419,984
	Operating income	49,669		66,758		97,804		68,061
	Net income	30,554		42,068		61,103		43,193
	Basic earnings per share	0.42		0.58		0.84		0.59
	Diluted earnings per share	0.42		0.58		0.84		0.59

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation
	Spirit Airlines, Inc. (Spirit or the Company) headquartered in Miramar, Florida, is an ultra low-cost, low-fare airline that provides affordable travel opportunities principally throughout the domestic United States, the Caribbean and Latin America. The Company manages operations on a system-wide basis due to the interdependence of its route structure in the various markets served. As only one service is offered (i.e., air transportation), management has concluded there is only one reportable segment.
	Certain prior period amounts have been reclassified to conform to the current year's presentation.
Use of Estimates	Use of Estimates
	The preparation of financial statements in accordance with generally accepted accounting principles in the United States of America requires the Company's management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The Company's estimates and assumptions are based on historical experience and changes in the business environment. However, actual results may differ from estimates under different conditions, sometimes materially. Critical accounting policies and estimates are defined as those that both (i) are most important to the portrayal of the Company's financial condition and results and (ii) require management's most subjective judgments. The Company's most critical accounting policies and estimates are described below.
Cash and Cash Equivalents	Cash and Cash Equivalents
	The Company considers all highly liquid investments with maturities of less than three months at the date of acquisition to be cash equivalents. Investments included in this category primarily consist of money market funds. Cash and cash equivalents are stated at cost, which approximates fair value.
Restricted Cash	Restricted Cash
	Restricted cash, when reported, consists of funds held by credit card processors as collateral for future travel paid with a credit card. As of December 31, 2014 and 2013, the Company held no restricted cash.
Accounts Receivable	Accounts Receivable
	Accounts receivable primarily consist of amounts due from credit card processors associated with the sales of tickets and amounts due from counterparties associated with fuel derivative instruments which have settled. The Company records an allowance for doubtful accounts for amounts not expected to be collected. The Company estimates the allowance based on historical write offs as well as aging trends. The allowance for doubtful accounts was immaterial as of December 31, 2014 and 2013.
	In addition, the provision for doubtful accounts and write-offs for 2014, 2013 and 2012 were each immaterial.
Property and Equipment	Property and Equipment
	Property and equipment is stated at cost, less accumulated depreciation and amortization. Depreciation of operating property and equipment is computed using the straight-line method applied to each unit of property. Residual values for aircraft, major spare rotable parts, avionics and assemblies are estimated to be 10%. Property under capital leases and related obligations are initially recorded at an amount equal to the present value of future minimum lease payments computed using the Company's incremental borrowing rate or, when known, the interest rate implicit in the lease. Amortization of property under capital leases is on a straight-line basis over the lease term and is included in depreciation and amortization expense.
	The depreciable lives used for the principal depreciable asset classifications are:
		Estimated Useful Life
	Aircraft	25 years
	Spare rotables and flight assemblies	7 to 15 years
	Other equipment and vehicles	5 to 7 years
	Internal use software	3 to 10 years
	Capital lease	Lease term
	Leasehold improvements	Lesser of lease term or estimated useful life of the improvement
	As of December 31, 2014, the Company had 4 aircraft capitalized within flight equipment with depreciable lives of 25 years and 61 aircraft financed through operating leases with terms of 3 to 15 years. All spare engines are financed through operating leases with terms of 7 to 12 years.
	In the third quarter of 2014, the Company purchased $13.5 million of rotable spare inventory which was previously rented. The cost to rent this inventory was recorded as maintenance, materials and repairs within the statement of operations. As a result of the purchase, the inventory was capitalized and the cost is amortized over the remaining useful life of the assets. The amortization is recorded as depreciation and amortization within the statement of operations.
	The following table illustrates the components of depreciation and amortization expense:
		Year Ended December 31,
		2014			2013			2012
		(in thousands)
	Depreciation	$	11,169		$	8,340		$	6,156
	Amortization of heavy maintenance	35,802			23,607			9,100
	Total depreciation and amortization	$	46,971		$	31,947		$	15,256
	The Company capitalizes certain internal and external costs associated with the acquisition and development of internal-use software for new products, and enhancements to existing products, that have reached the application development stage and meet recoverability tests. Capitalized costs include external direct costs of materials and services utilized in developing or obtaining internal-use software, and labor cost for employees who are directly associated with, and devote time, to internal-use software projects. Capitalized computer software, included as a component of ground and other equipment in the accompanying balance sheets, net of accumulated depreciation, was $7.4 million and $8.1 million at December 31, 2014 and 2013, respectively.
	Amortization of capitalized software costs is charged to depreciation on a straight-line method basis. Amortization of capitalized software costs was $3.5 million, $3.7 million and $3.2 million for the years ended 2014, 2013 and 2012, respectively. The Company placed in service internal-use software of $2.7 million, $7.0 million and $2.3 million, during the years ended 2014, 2013 and 2012, respectively.
Measurement of Asset Impairments	Measurement of Asset Impairments
	The Company records impairment charges on long-lived assets used in operations when events and circumstances indicate that the assets may be impaired, the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets, and the net book value of the assets exceeds their estimated fair value. In making these determinations, the Company uses certain assumptions, including, but not limited to: (i) estimated fair value of the assets; and (ii) estimated, undiscounted future cash flows expected to be generated by these assets, which are based on additional assumptions such as asset utilization, length of service the asset will be used in the Company’s operations, and estimated salvage values.
Passenger Revenue Recognition	Passenger Revenue Recognition
	Tickets sold are initially deferred as “air traffic liability.” Passenger revenue is recognized at time of departure when transportation is provided. A nonrefundable ticket expires at the date of scheduled travel and is recognized as revenue at the date of scheduled travel.
	Customers may elect to change their itinerary prior to the date of departure. A service charge is assessed and recognized on the date the change is initiated and is deducted from the face value of the original purchase price of the ticket, and the original ticket becomes invalid. The amount remaining after deducting the service charge is called a credit shell which expires 60 days from the date the credit shell is created and can be used towards the purchase of a new ticket and the Company’s other service offerings. The amount of credits expected to expire is recognized as revenue upon issuance of the credit and is estimated based on historical experience. Estimating the amount of credits that will go unused involves some level of subjectivity and judgment.
	The Company is also required to collect certain taxes and fees from customers on behalf of government agencies and airports and remit these back to the applicable governmental entity or airport on a periodic basis. These taxes and fees include U.S. federal transportation taxes, federal security charges, airport passenger facility charges and international arrival and departure taxes. These items are collected from customers at the time they purchase their tickets, but are not included in passenger revenue. The Company records a liability upon collection from the customer and relieves the liability when payments are remitted to the applicable governmental agency or airport.
Frequent Flier Program	Frequent Flier Program
	Flown Miles. The Company records unrecognized revenue for mileage credits earned by passengers under its FREE SPIRIT program, including mileage credits for members with an insufficient number of mileage credits to earn an award, based on the estimated incremental cost of providing free travel for credits that are expected to be redeemed. Incremental costs include fuel, insurance, security, ticketing and facility charges reduced by an estimate of fees required to be paid by the passenger when redeeming the award.
	Affinity Card Program. Under the Company's affinity card program, funds received for the marketing of a co-branded Spirit credit card and delivery of award miles are accounted for as a mulitple-deliverable arrangement. At the inception of the arrangement, the Company evaluated all deliverables in the arrangement to determine whether they represent separate units of accounting. The Company determined the arrangement had three separate units of accounting: (i) travel miles to be awarded, (ii) licensing of brand and access to member lists and (iii) advertising and marketing efforts. Arrangement consideration was allocated based on relative selling price. At inception of the arrangement, the Company established the relative selling price for all deliverables that qualified for separation. The manner in which the selling price was established was based on a hierarchy of evidence that the Company considered. Total arrangement consideration was then allocated to each deliverable on the basis of the deliverable’s relative selling price. In considering the hierarchy of evidence, the Company first determined whether vendor specific objective evidence of selling price or third-party evidence of selling price existed. It was determined by the Company that neither vendor specific objective evidence of selling price nor third-party evidence existed due to the uniqueness of the Company’s program. As such, the Company developed its best estimate of the selling price for all deliverables. For the award miles, the Company considered a number of entity-specific factors when developing the best estimate of the selling price including the number of miles needed to redeem an award, average fare of comparable segments, breakage, restrictions and other charges. For licensing of brand and access to member lists, the Company considered both market-specific factors and entity-specific factors including general profit margins realized in the marketplace/industry, brand power, market royalty rates and size of customer base. For the advertising element, the Company considered market-specific factors and entity-specific factors, including the Company’s internal costs (and fluctuations of costs) of providing services, volume of marketing efforts and overall advertising plan. Consideration allocated based on the relative selling price to both brand licensing and advertising elements is recognized as revenue when earned and recorded in non-ticket revenue. Consideration allocated to award miles is deferred and recognized ratably as passenger revenue over the estimated period the transportation is expected to be provided which is estimated at 14 months. The Company used entity-specific assumptions coupled with the various judgments necessary to determine the selling price of a deliverable in accordance with the required selling price hierarchy. Changes in these assumptions could result in changes in the estimated selling prices. Determining the frequency to reassess selling price for individual deliverables requires significant judgment. As of December 31, 2014, there have been no changes in either the selling price or the method or assumptions used to determine selling price for any of the identified units of accounting that would have a significant effect on the allocation of consideration.
Affinity Card Program, Multiple-deliverable arrangement	Affinity Card Program. Under the Company's affinity card program, funds received for the marketing of a co-branded Spirit credit card and delivery of award miles are accounted for as a mulitple-deliverable arrangement. At the inception of the arrangement, the Company evaluated all deliverables in the arrangement to determine whether they represent separate units of accounting. The Company determined the arrangement had three separate units of accounting: (i) travel miles to be awarded, (ii) licensing of brand and access to member lists and (iii) advertising and marketing efforts. Arrangement consideration was allocated based on relative selling price. At inception of the arrangement, the Company established the relative selling price for all deliverables that qualified for separation. The manner in which the selling price was established was based on a hierarchy of evidence that the Company considered. Total arrangement consideration was then allocated to each deliverable on the basis of the deliverable’s relative selling price. In considering the hierarchy of evidence, the Company first determined whether vendor specific objective evidence of selling price or third-party evidence of selling price existed. It was determined by the Company that neither vendor specific objective evidence of selling price nor third-party evidence existed due to the uniqueness of the Company’s program. As such, the Company developed its best estimate of the selling price for all deliverables. For the award miles, the Company considered a number of entity-specific factors when developing the best estimate of the selling price including the number of miles needed to redeem an award, average fare of comparable segments, breakage, restrictions and other charges. For licensing of brand and access to member lists, the Company considered both market-specific factors and entity-specific factors including general profit margins realized in the marketplace/industry, brand power, market royalty rates and size of customer base. For the advertising element, the Company considered market-specific factors and entity-specific factors, including the Company’s internal costs (and fluctuations of costs) of providing services, volume of marketing efforts and overall advertising plan. Consideration allocated based on the relative selling price to both brand licensing and advertising elements is recognized as revenue when earned and recorded in non-ticket revenue. Consideration allocated to award miles is deferred and recognized ratably as passenger revenue over the estimated period the transportation is expected to be provided which is estimated at 14 months. The Company used entity-specific assumptions coupled with the various judgments necessary to determine the selling price of a deliverable in accordance with the required selling price hierarchy. Changes in these assumptions could result in changes in the estimated selling prices. Determining the frequency to reassess selling price for individual deliverables requires significant judgment. As of December 31, 2014, there have been no changes in either the selling price or the method or assumptions used to determine selling price for any of the identified units of accounting that would have a significant effect on the allocation of consideration.
Non-ticket Revenue Recognition	Non-ticket Revenue Recognition
	Non-ticket revenues are generated from air travel-related services for baggage, bookings through the Company’s call center or third-party vendors, advance seat selection, itinerary changes and loyalty programs. Non-ticket revenues also consist of services not directly related to providing transportation such as the FREE SPIRIT affinity credit card program, $9 Fare Club and the sale of advertising to third parties on Spirit’s website and on board aircraft.
	The following table summarizes the primary components of non-ticket revenue and the revenue recognition method utilized for each service or product:
			Year Ended December 31,
	Non-ticket revenue	Recognition method	2014			2013			2012
			(in thousands)
	Baggage	Time of departure	$	318,103		$	275,958		$	217,536
	Passenger usage fee	Time of departure	221,992			188,911			149,577
	Advance seat selection	Time of departure	76,270			59,241			48,956
	Service charges for changes and cancellations	When itinerary is changed	38,388			32,546			27,762
	Other		131,855			111,711			91,765
	Non-ticket revenue		$	786,608		$	668,367		$	535,596
	Charges for services recognized at time of departure are initially recorded as a liability until time of departure. The passenger usage fee is charged for tickets sold through the Company’s primary sales distribution channels. The primary sales distribution channels for which passenger usage fees are charged include sales through the Company’s website, sales through the third-party provided call center and sales through travel agents; the Company does not charge a passenger usage fee for sales made at its airport ticket counters. Other non-ticket revenues include revenues from other air related charges as well as non-air related charges. Other air related charges include optional services and products provided to passengers such as on-board products, travel insurance and use of the Company’s call center or travel agents, among others. Non-air related charges primarily consist of revenues from advertising on the Company’s aircraft and website, the Company’s $9 Fare Club subscription-based membership program and the Company’s FREE SPIRIT affinity credit card program.
Airframe and Engine Maintenance	Airframe and Engine Maintenance
	The Company accounts for heavy maintenance and major overhaul and repair under the deferral method whereby the cost of heavy maintenance and major overhaul and repair is deferred and amortized until the earlier of the end of the remaining lease term or until the next scheduled heavy maintenance event.
	Amortization of heavy maintenance and major overhaul costs is charged to depreciation and amortization expense and was $35.8 million, $23.6 million and $9.1 million for the years ended 2014, 2013 and 2012, respectively. During the years ended 2014, 2013 and 2012, the Company deferred $33.6 million, $70.8 million and $61.6 million, respectively, of costs for heavy maintenance. At December 31, 2014 and 2013, the Company had deferred heavy maintenance balance of $198.9 million and $165.3 million, and accumulated heavy maintenance amortization of $75.8 million and $40.0 million, respectively.
	On October 15, 2013, a Company aircraft experienced an engine failure resulting in damage to the airframe and engine. In 2013, the Company expensed the insurance deductible related to this incident of approximately $0.8 million. As of December 31, 2014, the Company received insurance proceeds for a portion of the damage incurred. During 2014, the Company received a new replacement engine from the manufacturer in exchange for a $2.3 million payment to the manufacturer which was expensed within maintenance, materials and repairs in the statement of operations for the twelve months ended December 31, 2014.
	The Company outsources certain routine, non-heavy maintenance functions under contracts that require payment on a utilization basis, such as flight hours. Costs incurred for maintenance and repair under flight hour maintenance contracts, where labor and materials price risks have been transferred to the service provider, are expensed based on contractual payment terms. All other costs for routine maintenance of the airframes and engines are charged to expense as performed.
Leased Aircraft Return Costs	Leased Aircraft Return Costs
	The Company's aircraft lease agreements often contain provisions that require the Company to return aircraft airframes and engines to the lessor in a certain maintenance condition or pay an amount to the lessor based on the airframe and engine's actual return condition. Lease return costs, which could include cost to perform maintenance to airframes and engines to acceptable conditions prior to return, will be recognized as expense beginning when it is probable that such costs will be incurred and they can be estimated. Incurrence of lease return costs becomes probable and the amount of those costs can typically be estimated near the end of the lease term (that is, after the aircraft has completed its last maintenance cycle prior to being returned). The Company will evaluate all lease return conditions after the second to last maintenance event as it relates to the respective component or airframe from the lease return. If at this point it becomes both probable and estimable that a return cost will be incurred, the Company will accrue the cost on a straight-line basis as contingent rent through the remaining lease term. Return costs are recorded as a component of supplemental rent.
Aircraft Fuel	Aircraft Fuel
	Aircraft fuel expense includes jet fuel and associated “into-plane” costs, taxes, and oil, and realized and unrealized gains and losses associated with fuel derivative contracts.
Derivative Instruments	Derivative Instruments
	The Company accounts for derivative financial instruments at fair value and recognizes them in the balance sheet in prepaid expenses and other current assets or other current liabilities. For derivatives designated as cash flow hedges, changes in fair value of the derivative are generally reported in other comprehensive income and are subsequently reclassified into earnings when the hedged item affects earnings. On October 23, 2014, the Company entered into six forward interest rate swaps that fix the benchmark interest rate component of the forecasted interest payments on the debt related to three Airbus A321 aircraft with expected delivery dates ranging from July 2015 to September 2015 to limit the Company's exposure to changes in the benchmark interest rate in the period from the trade date through the aircraft delivery date. These interest rate swaps are designated as cash flow hedges. As a result, changes in the fair value of such derivatives are recorded within other accumulated comprehensive income.
	For the years ended 2014, 2013 and 2012, the Company did not hold fuel derivative instruments that were designated as cash flow hedges for accounting purposes. As a result, changes in the fair value of such fuel derivative contracts were recorded within aircraft fuel expense in the accompanying statements of operations. These amounts include both realized gains and losses and mark-to-market adjustments of the fair value of unsettled derivative instruments at the end of each period.
Advertising	Advertising
	The Company expenses advertising and the production costs of advertising as incurred.
Income Taxes	Income Taxes
	The Company accounts for income taxes using the liability method. The Company records a valuation allowance to reduce the deferred tax assets reported if, based on the weight of the evidence, it is more likely than not that some portion or all of the deferred tax assets will be not realized.
Stock-Based Compensation	Stock-Based Compensation
	The Company recognizes cost of employee services received in exchange for awards of equity instruments based on the fair value of each instrument at the date of grant. Compensation expense is recognized on a straight-line basis over the period during which an employee is required to provide service in exchange for an award. The Company has issued and outstanding restricted stock awards, stock option awards and performance share awards. Restricted stock awards are valued at the fair value of the shares on the date of grant. To the extent a market price was not available, the fair value of stock awards was estimated using a discounted cash flow analysis based on management’s estimates of revenue, driven by assumed market growth rates and estimated costs as well as appropriate discount rates. These estimates are consistent with the plans and estimates that management uses to manage the Company’s business. The fair value of share option awards is estimated on the date of grant using the Black-Scholes valuation model. The fair value of performance share awards is estimated through the use of a Monte Carlo simulation model.
Concentrations of Risk	Concentrations of Risk
	The Company’s business has been, and may continue to be, adversely affected by increases in the price of aircraft fuel, the volatility of the price of aircraft fuel, or both. Aircraft fuel was the Company’s single largest expenditure representing approximately 39%, 40% and 41% of total operating expenses in 2014, 2013 and 2012, respectively.
	The Company’s operations are largely concentrated in the southeast United States with Fort Lauderdale being the highest volume fueling point in the system. Gulf Coast Jet indexed fuel is the basis for a substantial majority of the Company’s fuel consumption. Any disruption to the oil production or refinery capacity in the Gulf Coast, as a result of weather or any other disaster, or disruptions in supply of jet fuel, dramatic escalations in the costs of jet fuel and/or the failure of fuel providers to perform under fuel arrangements for other reasons could have a material adverse effect on the Company’s financial condition and results of operations.
	The Company’s operations will continue to be vulnerable to weather conditions (including hurricane season or snow and severe winter weather), which could disrupt service, create air traffic control problems, decrease revenue and increase costs.
	Due to the relatively small size of the fleet and high utilization rate, the unavailability of one or more aircraft and resulting reduced capacity could have a material adverse effect on the Company’s business, results of operations and financial condition.
	As of December 31, 2014, the Company had four union-represented employee groups that together represented approximately 67% of all employees. As of December 31, 2013, the Company had three union-represented employee groups that together represented approximately 59% of all employees. A strike or other significant labor dispute with the Company’s unionized employees is likely to adversely affect the Company’s ability to conduct business.
Recent Accounting Developments	Recent Accounting Developments
	In May 2014, the Financial Accounting Standards Board (the FASB) issued Accounting Standards Update (ASU) No. 2014-09, (ASU 2014-09), "Revenue from Contracts with Customers." The objective of ASU 2014-09 is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and will supersede most of the existing revenue recognition guidance, including industry-specific guidance. The core principle of ASU 2014-09 is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying the new guidance, an entity will (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the contract's performance obligations; and (5) recognize revenue when (or as) the entity satisfies a performance obligation. ASU 2014-09 applies to all contracts with customers except those that are within the scope of other topics in the FASB Accounting Standards Codification. The new guidance is effective for annual reporting periods (including interim periods within those periods) beginning after December 15, 2016 for public companies. Early adoption is not permitted. Entities have the option of using either a full retrospective or modified approach to adopt ASU 2014-09. The Company is currently evaluating the new guidance and has not determined the impact this standard may have on its financial statements nor decided upon the planned method of adoption. While the Company is still evaluating the impact, it expects the accounting for its frequent flier program and certain ancillary fees to change.
Sale Leaseback Transactions	Deferred gains or losses from sale and leaseback transactions are amortized over the term of the lease as a reduction in rent or additional rent, respectively. Losses are deferred when the fair value of the aircraft or engine is higher than the price it was sold for, which is in substance, a prepayment of rent. A loss on disposal is recorded at the time of sale for the excess of the carrying amount over the fair value of the aircraft or engine.
Rent Expense, Deferred Gains (Losses)	Deferred losses are recognized as an increase to rent expense on a straight-line basis over the term of the respective operating leases. Deferred gains are included in deferred gains and other long-term liabilities on the accompanying balance sheet. Deferred gains are recognized as a decrease to rent expense on a straight-line basis over the term of the respective operating leases.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Depreciable lives used for the principal depreciable asset classifications	The following table illustrates the components of depreciation and amortization expense:
		Year Ended December 31,
		2014			2013			2012
		(in thousands)
	Depreciation	$	11,169		$	8,340		$	6,156
	Amortization of heavy maintenance	35,802			23,607			9,100
	Total depreciation and amortization	$	46,971		$	31,947		$	15,256
	The depreciable lives used for the principal depreciable asset classifications are:
		Estimated Useful Life
	Aircraft	25 years
	Spare rotables and flight assemblies	7 to 15 years
	Other equipment and vehicles	5 to 7 years
	Internal use software	3 to 10 years
	Capital lease	Lease term
	Leasehold improvements	Lesser of lease term or estimated useful life of the improvement
Total cash proceeds received from the sale of mileage credit	The following table illustrates total cash proceeds received from the sale of mileage credits and the portion of such proceeds recognized in revenue immediately as marketing component:
		Consideration received from credit card mile programs			Portion of proceeds recognized immediately as marketing component
	Year Ended	(in thousands)
	December 31, 2014	$	33,819		$	28,140
	December 31, 2013	28,496			23,124
	December 31, 2012	24,938			20,998
Primary components of non-ticket revenue and the revenue recognition method utilized for each service or product	The following table summarizes the primary components of non-ticket revenue and the revenue recognition method utilized for each service or product:
			Year Ended December 31,
	Non-ticket revenue	Recognition method	2014			2013			2012
			(in thousands)
	Baggage	Time of departure	$	318,103		$	275,958		$	217,536
	Passenger usage fee	Time of departure	221,992			188,911			149,577
	Advance seat selection	Time of departure	76,270			59,241			48,956
	Service charges for changes and cancellations	When itinerary is changed	38,388			32,546			27,762
	Other		131,855			111,711			91,765
	Non-ticket revenue		$	786,608		$	668,367		$	535,596
Aircraft maintenance expense	The table below summarizes the extent to which the Company’s maintenance costs are rate capped due to flight hour maintenance contracts:
		Year Ended December 31,
		2014			2013			2012
		(in thousands)
	Flight hour-based maintenance expense	$	35,675		$	30,322		$	25,748
	Non-flight hour-based maintenance expense	38,281			29,821			23,712
	Total maintenance, materials and repairs	$	73,956		$	60,143		$	49,460

Accrued_Liabilities_Tables

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
Accrued liabilities included in other current liabilities	Accrued liabilities included in other current liabilities as of December 31, 2014 and 2013 consist of the following:
		As of December 31,
		2014		2013
		(in thousands)
	Federal excise and other passenger taxes and fees payable	$	42,628	$	26,979
	Salaries and wages	34,209		26,174
	Airport expenses	21,726		17,109
	Aircraft maintenance	16,127		36,165
	Aircraft and facility rent	10,089		7,993
	Fuel	9,508		13,819
	Federal and state income tax payable	3,286		794
	Tax Receivable Agreement	—		5,643
	Other	15,348		10,586
	Other current liabilities	$	152,921	$	145,262

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of the status of the Company's restricted stock shares	A summary of the status of the Company’s restricted stock shares (restricted stock awards and restricted stock unit awards) as of December 31, 2014 and changes during the year ended December 31, 2014 is presented below:
		Number of Shares			Weighted-Average
					Grant Date Fair Value ($)
	Outstanding at December 31, 2013	336,048			22.99
	Granted	182,464			55.14
	Vested	(111,782	)		22.96
	Forfeited	(42,839	)		25.47
	Outstanding at December 31, 2014	363,891			38.83
Summary of share option activity	A summary of share option activity under the 2011 Plan as of December 31, 2014 and changes during the year ended December 31, 2014 is presented below:
		Number			Weighted-		Average	Aggregate
		of Options			Average		Remaining	Intrinsic
					Exercise		Contractual	Value
					Price ($)		Term	$0
							(Years)
	Outstanding at December 31, 2013	56,500			8.26		6.7	2,099
	Exercised	(21,125	)		8.18
	Forfeited or expired	(3,750	)		8.21
	Outstanding at December 31, 2014	31,625			8.32		5.7	2,127
	Exercisable at December 31, 2014	30,875			8.22		5.7	2,080
	Vested or Expected to Vest at December 31, 2014	31,614			8.32		5.7	2,126
Multiple input variables of performance share awards	The grant date fair value of the performance share awards was determined through the use of a Monte Carlo simulation model, which utilizes multiple input variables that determine the probability of satisfying the market condition requirements applicable to each award as follows:
		Weighted-Average at Grant Date for Twelve Months Ended December 31, 2014			Weighted-Average at Grant Date for Twelve Months Ended December 31, 2013
	Expected volatility factor	0.42			0.41
	Risk free interest rate	0.65		%	0.33	%
	Expected term (in years)	2.77			2.65
	Expected dividend yield	—		%	—	%
Performance share award activity	The following table summarizes the Company’s performance share awards for the year ended December 31, 2014:
		Number of Awards			Weighted-Average Fair Value at Grant Date ($)
	Outstanding at December 31, 2013	327,104			22.94
	Granted	53,841			59.45
	Vested	(185,907	)		20.4
	Forfeited	(52,468	)		23.92
	Outstanding at December 31, 2014	142,570			39.67

Net_Income_per_Share_Tables

Net Income per Share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Computation of basic and diluted earnings per common share	The following table sets forth the computation of basic and diluted earnings per common share:
		Year Ended December 31,
		2014		2013		2012
		(in thousands, except per share amounts)
	Numerator:
	Net income	$	225,464	$	176,918	$	108,460
	Denominator:
	Weighted-average shares outstanding, basic	72,739		72,593		72,386
	Effect of dilutive stock awards	555		406		205
	Adjusted weighted-average shares outstanding, diluted	73,294		72,999		72,591
	Net Income per Share:
	Basic earnings per common share	$	3.1	$	2.44	$	1.5
	Diluted earnings per common share	$	3.08	$	2.42	$	1.49
	Anti-dilutive weighted-average shares	29		1		88

Debt_and_Other_Obligations_Tab

Debt and Other Obligations (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Schedule of long-term debt instruments	Long-term debt is comprised of the following:
			As of December 31,
			2014			2013		2014		2013
			(in millions)					(weighted-average interest rates)
	Senior Term Loans due through 2026		$	132		$	—	4.26	%	N/A
	Junior Term Loans due through 2021		16			—		6.94	%	N/A
	Long-term debt		$	148		$	—
	Less current maturities		10.4			—
	Less unamortized discount, net		1.8			—
	Total		$	135.8		$	—
Schedule of maturities of long-term debt	At December 31, 2014, long-term debt principal payments for the next five years and thereafter are as follows:
			December 31, 2014
			(in millions)
	2015		$	10.4
	2016		10.9
	2017		11.6
	2018		12
	2019		12.6
	2020 and thereafter		90.5
	Total debt principal payments		$	148
Schedule of interest expense on long-term debt	Interest expense related to debt consists of the following:
		Year Ended December 31,
		2014			2013
		(in thousands)
	Senior Term Loans	$	738		$	—
	Junior Term Loans	145			—
	Commitment fees	685			—
	Amortization of deferred financing costs	9			—
	Total	$	1,577		$	—
Schedule of future minimum lease payments for capital leases	Aggregate annual principal maturities of capital leases as of December 31, 2014 and December 31, 2013 are as follows:
			As of December 31,
			2014			2013
			(in thousands)
	2015		$	1,289		$	1,083
	2016		1,002			966
	2017		39			—
	2018		42			—
	2019		11			—
	2020 and thereafter		—			—
	Total principal maturities		$	2,383		$	2,049
	Future minimum lease payments under capital leases and noncancellable operating leases with initial or remaining terms in excess of one year at December 31, 2014 were as follows:
						Operating Leases
			Capital Leases			Aircraft and Spare Engine Leases		Property Facility Leases			Total Operating Leases
			(in thousands)
	2015		$	1,444		$	214,337	$	29,647		$	243,984
	2016		1,044			212,512		25,239			237,751
	2017		44			196,010		25,613			221,623
	2018		44			172,323		25,759			198,082
	2019		12			144,211		23,606			167,817
	2020 and thereafter		—			592,409		71,578			663,987
	Total minimum lease payments		$	2,588		$	1,531,802	$	201,442		$	1,733,244
	Less amount representing interest		205
	Present value of minimum lease payments		2,383
	Less current portion		1,289
	Long-term portion		1,094

Leases_and_Prepaid_Maintenance1

Leases and Prepaid Maintenance Deposits (Tables)	12 Months Ended
	Dec. 31, 2014
Leases [Abstract]
Schedule of capital leased assets	Amounts applicable to these QEC kits that are included in property and equipment were:
		2014		2013
		(in thousands)
	Flight equipment	$	3,234	$	3,234
	Less: accumulated amortization	377		54
		$	2,857	$	3,180
Schedule of future minimum lease payments for capital leases	Aggregate annual principal maturities of capital leases as of December 31, 2014 and December 31, 2013 are as follows:
		As of December 31,
		2014		2013
		(in thousands)
	2015	$	1,289	$	1,083
	2016	1,002		966
	2017	39		—
	2018	42		—
	2019	11		—
	2020 and thereafter	—		—
	Total principal maturities	$	2,383	$	2,049
	Future minimum lease payments under capital leases and noncancellable operating leases with initial or remaining terms in excess of one year at December 31, 2014 were as follows:
				Operating Leases
		Capital Leases		Aircraft and Spare Engine Leases		Property Facility Leases		Total Operating Leases
		(in thousands)
	2015	$	1,444	$	214,337	$	29,647	$	243,984
	2016	1,044		212,512		25,239		237,751
	2017	44		196,010		25,613		221,623
	2018	44		172,323		25,759		198,082
	2019	12		144,211		23,606		167,817
	2020 and thereafter	—		592,409		71,578		663,987
	Total minimum lease payments	$	2,588	$	1,531,802	$	201,442	$	1,733,244
	Less amount representing interest	205
	Present value of minimum lease payments	2,383
	Less current portion	1,289
	Long-term portion	1,094
Schedule of future minimum rental payments for noncancellable operating leases	Future minimum lease payments under capital leases and noncancellable operating leases with initial or remaining terms in excess of one year at December 31, 2014 were as follows:
				Operating Leases
		Capital Leases		Aircraft and Spare Engine Leases		Property Facility Leases		Total Operating Leases
		(in thousands)
	2015	$	1,444	$	214,337	$	29,647	$	243,984
	2016	1,044		212,512		25,239		237,751
	2017	44		196,010		25,613		221,623
	2018	44		172,323		25,759		198,082
	2019	12		144,211		23,606		167,817
	2020 and thereafter	—		592,409		71,578		663,987
	Total minimum lease payments	$	2,588	$	1,531,802	$	201,442	$	1,733,244
	Less amount representing interest	205
	Present value of minimum lease payments	2,383
	Less current portion	1,289
	Long-term portion	1,094

Financial_Instruments_and_Risk1

Financial Instruments and Risk Management (Tables)	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Components of aircraft fuel expense	The following table summarizes the components of aircraft fuel expense for the years ended December 31, 2014, 2013 and 2012:
		Year Ended December 31,
		2014		2013		2012
		(in thousands)
	Into-plane fuel cost	$	608,033	$	542,523	$	471,542
	Realized losses (gains)	995		8,958		175
	Unrealized mark-to-market losses (gains)	3,881		265		46
	Aircraft fuel	$	612,909	$	551,746	$	471,763

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Significant components of the provision for income taxes from continuing operations	Significant components of the provision for income taxes from continuing operations are as follows:
		Year Ended December 31,
		2014				2013				2012
		(in thousands)
	Current:
	Federal	$	85,966			$	86,437			$	32,656
	State and local	5,389				6,595				3,250
	Foreign	2,057				413				963
	Total current expense	93,412				93,445				36,869
	Deferred:
	Federal	34,240				11,658				27,870
	State and local	(122		)		389				1,385
	Total deferred expense (benefit)	34,118				12,047				29,255
	Total income tax expense (benefit)	$	127,530			$	105,492			$	66,124
Reconciliation of income tax expense	The income tax provision differs from that computed at the federal statutory corporate tax rate as follows:
		Year Ended December 31,
		2014			2013			2012
	Expected provision at federal statutory tax rate	35	%		35	%		35	%
	State tax expense, net of federal benefit	1	%		1.7	%		2.1	%
	Income tax credits	(0.4	)%		—	%		(0.1	)%
	Other	0.5	%		0.7	%		0.9	%
	Total income tax expense (benefit)	36.1	%		37.4	%		37.9	%
Deferred taxes	At December 31, 2014 and 2013, the significant components of the Company's deferred taxes consisted of the following:
		December 31,
		2014				2013
		(in thousands)
	Deferred tax assets:
	Net operating loss	$	252			$	188
	Accrued rent	—				1,872
	Deferred revenue	410				6,241
	Nondeductible accruals	12,239				6,702
	Deferred manufacturing credits	848				3,309
	Unrealized gains/losses on derivatives	1,865				—
	Accrued maintenance	3,073				1,225
	Equity compensation	4,514				2,687
	Other	661				16
	Deferred tax assets	23,862				22,240
	Deferred tax liabilities:
	Capitalized interest	568				736
	Deferred gain and losses on leases, net	2,349				1,882
	Accrued rent	2,560				—
	Prepaid expenses	1,681				—
	Property, plant and equipment	37,369				6,384
	Accrued engine maintenance	45,702				45,911
	Deferred tax liabilities	90,229				54,913
	Net deferred tax assets (liabilities)	$	(66,367	)		$	(32,673	)
	Deferred taxes included within:
	Assets:
	Current deferred tax assets, net	$	9,643			$	16,243
	Liabilities:
	Noncurrent deferred tax liabilities, net	$	76,010			$	48,916

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Operating Aircraft Leases	As of December 31, 2014, the Company's aircraft orders consisted of the following:
		Airbus				Third-Party Lessor
		A320	A320NEO	A321	A321NEO	A320NEO	Total
	2015	8		6		1	15
	2016	3		9		4	16
	2017	8		10			18
	2018	2	6	5			13
	2019		3		10		13
	2020		13				13
	2021		18				18
		21	40	30	10	5	106
Schedules of Concentration of Risk, by Risk Factor	The table below sets forth the Company's employee groups and status of the collective bargaining agreements as of December 31, 2014.
	Employee Groups	Representative	Amendable Date	Percentage of Workforce
	Pilots	Air Line Pilots Association, International (ALPA)	August 2015	25%
	Flight Attendants	Association of Flight Attendants (AFA-CWA)	Aug-07	35%
	Dispatchers	Transport Workers Union (TWU)	Aug-18	1%
	Ramp Service Agents	International Association of Machinists and Aerospace Workers (IAM)	TBD	6%

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Long-term debt measured at fair value	The carrying amounts and estimated fair values of our long-term debt at December 31, 2014 were as follows:
		Carrying value			Estimated fair value
		(in millions)
	Senior long-term debt	$	132		$	132
	Junior long-term debt	16			16.1
	Total long-term debt	$	148		$	148.1
Assets and liabilities measured at fair value on a recurring basis	Assets and liabilities measured at gross fair value on a recurring basis are summarized below:
		Fair Value Measurements as of December 31, 2014
		Total			Level		Level		Level
					1		2		3
		(in millions)
	Cash and cash equivalents	$	632.8		$	632.8	$	—	$	—
	Jet fuel options	4.8			—		—		4.8
	Total assets	$	637.6		$	632.8	$	—	$	4.8
	Interest rate swaps	$	1.1		$	—	$	1.1	$	—
	Total liabilities	$	1.1		$	—	$	1.1	$	—
		Fair Value Measurements as of December 31, 2013
		Total			Level		Level		Level
					1		2		3
		(in millions)
	Cash and cash equivalents	$	530.6		$	530.6	$	—	$	—
	Total assets	$	530.6		$	530.6	$	—	$	—
	Total liabilities	$	—		$	—	$	—	$	—
Assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (level 3)	The following table presents the Company’s activity for assets and liabilities measured at gross fair value on a recurring basis using significant unobservable inputs (Level 3):
		Jet Fuel Options
		(in millions)
	Balance at January 1, 2012	$	0.3
	Total realized or unrealized gains (losses) included in earnings, net	(0.2		)
	Purchases	—
	Sales	—
	Settlements, net	0.2
	Balance at December 31, 2012	0.3
	Total realized or unrealized gains (losses) included in earnings, net	0.1
	Purchases	—
	Sales	—
	Settlements, net	(0.4		)
	Balance at December 31, 2013	—
	Total realized or unrealized gains (losses) included in earnings, net	(4.9		)
	Purchases	9.7
	Sales	—
	Settlements, net	—
	Balance at December 31, 2014	$	4.8

Operating_Segments_and_Related1

Operating Segments and Related Disclosures (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Operating revenues by geographic region	Operating revenues by geographic region as defined by the Department of Transportation (DOT) area are summarized below:
		2014		2013		2012
		(in millions)
	DOT—domestic	$	1,728.80	$	1,467.50	$	1,135.10
	DOT—Latin America	202.8		186.9		183.3
	Total	$	1,931.60	$	1,654.40	$	1,318.40

Quarterly_Financial_Data_Unaud1

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly results of operations	Quarterly results of operations for the years ended December 31, 2014 and 2013 are summarized below:
		Three Months Ended
		31-Mar		30-Jun		30-Sep		31-Dec
		(in thousands, except per share amounts)
	2014
	Operating revenue	$	437,987	$	499,337	$	519,769	$	474,487
	Operating income	59,953		105,144		100,191		89,975
	Net income	37,706		64,849		67,000		55,909
	Basic earnings per share	0.52		0.89		0.92		0.77
	Diluted earnings per share	0.51		0.88		0.91		0.76
	2013
	Operating revenue	$	370,437	$	407,339	$	456,625	$	419,984
	Operating income	49,669		66,758		97,804		68,061
	Net income	30,554		42,068		61,103		43,193
	Basic earnings per share	0.42		0.58		0.84		0.59
	Diluted earnings per share	0.42		0.58		0.84		0.59

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Reportable Segments (Details)	12 Months Ended
	Dec. 31, 2014
	segment
Accounting Policies [Abstract]
Number of reportable segments	1

Summary_of_Significant_Account4

Summary of Significant Accounting Policies - Property and Equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014
Property, Plant and Equipment [Line Items]
Rotable spare inventory, purchased				$13,500,000
Depreciation, Depletion and Amortization, Nonproduction [Abstract]
Depreciation	11,169,000	8,340,000	6,156,000
Amortization of heavy maintenance	35,802,000	23,607,000	9,100,000
Total depreciation and amortization	46,971,000	31,947,000	15,256,000
Amortization of capitalized software costs	3,500,000	3,700,000	3,200,000
Aircraft
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	25 years
Number of aircraft capitalized	4
Number of aircraft under operating lease	61
Aircraft | Minimum
Property, Plant and Equipment [Line Items]
Operating leases, term	3 years
Aircraft | Maximum
Property, Plant and Equipment [Line Items]
Operating leases, term	15 years
Spare rotables and flight assemblies
Property, Plant and Equipment [Line Items]
Residual value, percentage	10.00%
Spare rotables and flight assemblies | Minimum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	7 years
Spare rotables and flight assemblies | Maximum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	15 years
Other equipment and vehicles | Minimum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	5 years
Other equipment and vehicles | Maximum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	7 years
Internal use software
Depreciation, Depletion and Amortization, Nonproduction [Abstract]
Capitalized computer software, net	7,400,000	8,100,000
Capitalized software costs during the year	$2,700,000	$7,000,000	$2,300,000
Internal use software | Minimum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	3 years
Internal use software | Maximum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	10 years
Spare engines
Property, Plant and Equipment [Line Items]
Number of aircraft under operating lease	10
Spare engines | Minimum
Property, Plant and Equipment [Line Items]
Operating leases, term	7 years
Spare engines | Maximum
Property, Plant and Equipment [Line Items]
Operating leases, term	12 years

Summary_of_Significant_Account5

Summary of Significant Accounting Policies - Frequent Flier Program (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
	unit_of_accounting
Accounting Policies [Abstract]
Credit shell, term of expiration	60 days
Number of units of accounting	3
Affinity Card Program, deferred fair value of the transportation component, recognition period	14 months
Liability for future FREE SPIRIT award redemptions and unrecognized revenue from the sale of mileage credits	$2.80	$2.60

Summary_of_Significant_Account6

Summary of Significant Accounting Policies - Cash Proceeds Received from the Sale of Mileage Credits (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Consideration received from credit card mile programs	$33,819	$28,496	$24,938
Portion of proceeds recognized immediately as marketing component	$28,140	$23,124	$20,998

Summary_of_Significant_Account7

Summary of Significant Accounting Policies - Primary Components of Non-Ticket Revenue (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Product Information [Line Items]
Non-ticket revenue	$786,608	$668,367	$535,596
Baggage
Product Information [Line Items]
Non-ticket revenue	318,103	275,958	217,536
Passenger usage fee
Product Information [Line Items]
Non-ticket revenue	221,992	188,911	149,577
Advance seat selection
Product Information [Line Items]
Non-ticket revenue	76,270	59,241	48,956
Service charges for changes and cancellations
Product Information [Line Items]
Non-ticket revenue	38,388	32,546	27,762
Other
Product Information [Line Items]
Non-ticket revenue	$131,855	$111,711	$91,765

Summary_of_Significant_Account8

Summary of Significant Accounting Policies - Maintenance Costs (Details) (USD $)	0 Months Ended	12 Months Ended
	Oct. 15, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Amortization of heavy maintenance		$35,802,000	$23,607,000	$9,100,000
Deferred costs for heavy maintenance		33,600,000	70,800,000	61,600,000
Deferred heavy maintenance, gross		198,900,000	165,300,000
Accumulated heavy maintenance amortization		75,800,000	40,000,000
Insurance deductible	800,000
Engine, replacement expense		2,300,000
Airframe and Engine Maintenance Costs [Abstract]
Flight hour-based maintenance expense		35,675,000	30,322,000	25,748,000
Non-flight hour-based maintenance expense		38,281,000	29,821,000	23,712,000
Total maintenance, materials and repairs		$73,956,000	$60,143,000	$49,460,000

Summary_of_Significant_Account9

Summary of Significant Accounting Policies - Narrative (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 23, 2014
	employee_group	employee_group		derivative_instrument
	aircraft
Concentration Risk [Line Items]
Future aircraft to be received, next twelve months	15
Marketing and advertising expenses	$3	$2.10	$2.40
Union-represented employee groups	4	3
Aircraft fuel expenditure concentration risk | Total operating expenses
Concentration Risk [Line Items]
Concentration of risk	39.00%	40.00%	41.00%
Unionized employees concentration risk | Number of employees, total
Concentration Risk [Line Items]
Concentration of risk	67.00%	59.00%
Union-represented employee groups		3
Interest rate swap
Concentration Risk [Line Items]
Number of forward interest rate swaps				6

Special_Charges_and_Credits_De

Special Charges and Credits (Details) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
				aircraft_slot
Special Charges and Credits [Abstract]
Number of permanent air carrier slots transferred				4
Proceeds from sale of slots		$0	$0	$9,060
Gain on slot sale	$9,100	$0	$0	$9,060

Letters_of_Credit_Details

Letters of Credit (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Line of Credit Facility [Line Items]
Posted letters of credit	$0.20	$0.20
Unsecured, standby letter of credit facility
Line of Credit Facility [Line Items]
Letters of credit, limit, amount	25.1
Letter of credit facility, amount outstanding	$10.30

Credit_Card_Processing_Arrange1

Credit Card Processing Arrangements (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Credit Card Processing Arrangements [Abstract]
Cash holdbacks	$0	$0
Maximum potential exposure to cash holdbacks by the credit card processors	$217,100,000	$188,600,000

Accrued_Liabilities_Details

Accrued Liabilities (Details) (USD $)	Dec. 31, 2014	Jun. 17, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Payables and Accruals [Abstract]
Federal excise and other passenger taxes and fees payable	$42,628		$26,979
Salaries and wages	34,209		26,174
Airport expenses	21,726		17,109
Aircraft maintenance	16,127		36,165
Aircraft and facility rent	10,089		7,993
Fuel	9,508		13,819
Federal and state income tax payable	3,286		794
Current Portion of Estimated Remaining Cash Payment to Pre-Initial Public Offering Stockholders	0	5,600	5,643	8,000
Other	15,348		10,586
Other current liabilities	$152,921		$145,262

Common_Stock_and_Preferred_Sto1

Common Stock and Preferred Stock (Details) (USD $)	0 Months Ended
	Dec. 07, 2011	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Preferred stock, shares authorized		10,000,000
Preferred stock, par value (in dollars per share)		$0.00
Preferred stock, shares outstanding		0	0
Voting Common Stock
Class of Stock [Line Items]
Common stock, shares authorized		240,000,000	240,000,000
Common stock, par value (in dollars per share)		$0.00	$0.00
Common stock, shares outstanding		72,775,685	72,670,673
Non-Voting Common Stock
Class of Stock [Line Items]
Common stock, shares authorized		50,000,000	50,000,000
Common stock, par value (in dollars per share)		$0.00	$0.00
Stock distribution agreement, common stock were exchanged on a share-for-share basis for shares of non-voting common stock	10,576,180
Common stock, shares outstanding		0	0

StockBased_Compensation_Narrat

Stock-Based Compensation - Narrative (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2007	9-May-11
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation cost	$8.80	$5.70	$4.30
Share-based compensation cost, tax benefit recognized in income	$3.20	$2.10	$1.60
2005 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issue (in shares)				2,500,000
2011 Equity Incentive Award Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issue (in shares)					3,000,000
Shares available for future issuance (in shares)	2,682,457	2,789,276

StockBased_Compensation_Restri

Stock-Based Compensation - Restricted Stock Activity (Details) (Restricted Stock [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage per year	25.00%
Period for share issuance after vesting	30 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding (in shares)	336,048
Granted (in shares)	182,464	151,202
Vested (in shares)	-111,782
Forfeited (in shares)	-42,839
Outstanding (in shares)	363,891	336,048
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding, weighted-average grant date fair value (in dollars per share)	$22.99
Granted, weighted-average grant date fair value (in dollars per share)	$55.14	$27.70	$20.01
Vested, weighted-average grant date fair value (in dollars per share)	$22.96
Forfeited, weighted-average grant date fair value (in dollars per share)	$25.47
Outstanding, weighted-average grant date fair value (in dollars per share)	$38.83	$22.99
Total compensation cost not yet recognized	$10,600,000	$6,100,000
Total compensation cost not yet recognized, period for recognition	2 years 9 months 10 days	2 years 8 months 12 days
Total fair value of shares vested	$6,500,000	$4,300,000	$3,900,000

StockBased_Compensation_Share_

Stock-Based Compensation - Share Option Activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period (in shares)	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding (in shares)	56,500
Exercised (in shares)	-21,125
Forfeited or expired (in shares)	-3,750
Outstanding (in shares)	31,625	56,500
Exercisable (in shares)	30,875
Vested or expected to vest (in shares)	31,614
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, weighted-average exercise price (in dollars per share)	$8.26
Exercised, weighted-average exercise price (in dollars per share)	$8.18
Forfeited or expired, weighted-average exercise price (in dollars per share)	$8.21
Outstanding, weighted-average exercise price (in dollars per share)	$8.32	$8.26
Exercisable, weighted-average exercise price (in dollars per share)	$8.22
Vested or expected to vest, weighted-average exercise price (in dollars per share)	$8.32
Outstanding, average remaining contractual term (in years)	5 years 8 months 24 days	6 years 8 months 12 days
Exercisable, average remaining contractual term (in years)	5 years 8 months 24 days
Vested or expected to vest, average remaining contractual term	5 years 8 months 24 days
Outstanding, aggregate intrinsic value	$2,127,000	$2,099,000
Exercisable, aggregate intrinsic value	2,080,000
Vested or expected to vest, aggregate intrinsic value	2,126,000
Total intrinsic value of share options exercised	1,300,000	2,000,000	700,000
Options, vested in period, fair value	100,000	200,000	400,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Contractual term	10 years
Grants in period (in shares)		0	0
Expected volatility factor				46.25%
Expected dividend yield (percent)				0.00%
Expected term (in years)				6 years 3 months
Risk free interest rate (percent)				2.03%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Total compensation cost not yet recognized	$3,100	$46,700
Total compensation cost not yet recognized, period for recognition	8 months 12 days	9 months 10 days

StockBased_Compensation_Simula

Stock-Based Compensation - Simulation Model Input Variables (Details) (Performance Shares Awards)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Performance Shares Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility factor	0.42%	0.41%
Risk free interest rate (percent)	0.65%	0.33%
Expected term (in years)	2 years 9 months 8 days	2 years 7 months 23 days
Expected dividend yield (percent)	0.00%	0.00%

StockBased_Compensation_Perfor

Stock-Based Compensation - Performance Share Awards (Details) (Performance Shares Awards, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite performance period	3 years
Period for share issuance after vesting	60 days
Expected dividend yield (percent)	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding (in shares)	327,104
Granted (in shares)	53,841
Vested (in shares)	-185,907
Forfeited (in shares)	-52,468
Outstanding (in shares)	142,570	327,104
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding, weighted-average grant date fair value (in dollars per share)	$22.94
Granted, weighted-average grant date fair value (in dollars per share)	$59.45
Vested, weighted-average grant date fair value (in dollars per share)	$20.40
Forfeited, weighted-average grant date fair value (in dollars per share)	$23.92
Outstanding, weighted-average grant date fair value (in dollars per share)	$39.67	$22.94
Total compensation cost not yet recognized	$4,500,000	$6,500,000
Total compensation cost not yet recognized, period for recognition	1 year 7 months 20 days	1 year 6 months 15 days
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential vesting percentage	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential vesting percentage	200.00%

Net_Income_per_Share_Details

Net Income per Share (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income	$55,909	$67,000	$64,849	$37,706	$43,193	$61,103	$42,068	$30,554	$225,464	$176,918	$108,460
Denominator:
Weighted-average shares outstanding, basic (in shares)									72,739	72,593	72,386
Effect of dilutive stock awards (in shares)									555	406	205
Adjusted weighted-average shares outstanding, diluted (in shares)									73,294	72,999	72,591
Net Income per Share:
Basic earnings per common share (in dollars per share)	$0.77	$0.92	$0.89	$0.52	$0.59	$0.84	$0.58	$0.42	$3.10	$2.44	$1.50
Diluted earnings per common share (in dollars per share)	$0.76	$0.91	$0.88	$0.51	$0.59	$0.84	$0.58	$0.42	$3.08	$2.42	$1.49
Antidilutive awards excluded from computation of earnings per common share (in shares)									29	1	88

Debt_and_Other_Obligations_Nar

Debt and Other Obligations - Narrative (Details) (USD $)	12 Months Ended		0 Months Ended	2 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Oct. 01, 2014	Feb. 18, 2015
				aircraft
Line of Credit Facility [Line Items]
Maximum borrowing capacity			379,000,000
Long-term debt, gross	148,000,000	0
Unamortized deferred finance costs	700,000
Unamortized deferred financing costs		0
Commitment fees	685,000	0
Corporate credit cards
Line of Credit Facility [Line Items]
Maximum borrowing capacity	18,600,000	18,600,000
Line of credit, outstanding	4,500,000	3,700,000
Aircraft fuel
Line of Credit Facility [Line Items]
Maximum borrowing capacity	38,000,000	34,500,000
Line of credit, outstanding	9,300,000	13,800,000
Quick Engine Change Kit
Line of Credit Facility [Line Items]
Number of units under capital lease	2
Senior loans
Line of Credit Facility [Line Items]
Debt instrument, term			12 years
Long-term debt, gross	132,000,000	0
Annual commitment fee (percent)	0.75%
Junior loans
Line of Credit Facility [Line Items]
Debt instrument, term			7 years
Long-term debt, gross	16,000,000	0
Annual commitment fee (percent)	1.25%
Airbus
Line of Credit Facility [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery	6
Airbus | A320
Line of Credit Facility [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery	3		7
Number of delivered aircraft with secured debt financing commitments	4
Commitment fees	200,000
Airbus | A320 | Subsequent event
Line of Credit Facility [Line Items]
Number of aircrafts delivered				2
Long-term debt outstanding				74,000,000
Airbus | A321
Line of Credit Facility [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery	3		3
Airbus | A320 and A321
Line of Credit Facility [Line Items]
Commitment fees	$500,000

Debt_and_Other_Obligations_Lon

Debt and Other Obligations - Long-term Debt (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt, gross	$148,000,000	$0
Less current maturities	10,431,000	0
Less unamortized discount, net	1,800,000	0
Total	135,817,000	0
Senior loans
Debt Instrument [Line Items]
Long-term debt, gross	132,000,000	0
Weighted-average interest rates	4.26%
Junior loans
Debt Instrument [Line Items]
Long-term debt, gross	$16,000,000	$0
Weighted-average interest rates	6.94%

Debt_and_Other_Obligations_Fut

Debt and Other Obligations - Future Maturities (Details) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Debt Disclosure [Abstract]
2015	$10.40
2016	10.9
2017	11.6
2018	12
2019	12.6
2020 and thereafter	90.5
Long-term debt	$148

Debt_and_Other_Obligations_Int

Debt and Other Obligations - Interest Expense (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Commitment fees	$685	$0
Amortization of deferred financing costs	9	0
Interest expense	1,577	0
Senior loans
Debt Instrument [Line Items]
Interest expense, debt	738	0
Junior loans
Debt Instrument [Line Items]
Interest expense, debt	$145	$0

Debt_and_Other_Obligations_Cap

Debt and Other Obligations - Capital Leases (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Debt Disclosure [Abstract]
2015	$1,289	$1,083
2016	1,002	966
2017	39	0
2018	42	0
2019	11	0
2020 and thereafter	0	0
Present value of minimum lease payments	$2,383	$2,049

Leases_and_Prepaid_Maintenance2

Leases and Prepaid Maintenance Deposits - Operating Leases (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Leased Assets [Line Items]
Total rental expense	$254,300,000	$214,600,000	$178,400,000
Rental expense charged to operations for aircraft and engine operating leases	195,827,000	169,737,000	143,572,000
Aircraft maintenance deposits	250,000,000	220,700,000
Maintenance reserves, supplemental rent	1,600,000	1,900,000	2,000,000
Prepaid Expenses and Other Current Assets
Operating Leased Assets [Line Items]
Prepaid aircraft maintenance to lessors, current	36,900,000	59,200,000
Fixed Maintenance Reserve Payments | Aircraft and Related Flight Equipment
Operating Leased Assets [Line Items]
Committed expenditures, 2015	7,600,000
Committed expenditures, 2016	8,000,000
Committed expenditures, 2017	7,400,000
Committed expenditures, 2018	5,800,000
Committed expenditures, 2019	4,200,000
Committed expenditures, 2020 and beyond	14,100,000
Aircraft rent
Operating Leased Assets [Line Items]
Supplemental rent expense	$7,500,000	$5,200,000	$2,000,000
Aircraft
Operating Leased Assets [Line Items]
Number of aircraft and spare engines financed under operating leases	61
Number of aircraft and spare engines financed under operating leases with a variable rate	5
Number of aircraft leases available for renewal	3
Aircraft operating leases, renewal term	3 years
Aircraft operating leases, period before renewal	10 years
Aircraft | Minimum
Operating Leased Assets [Line Items]
Operating leases, term	3 years
Aircraft | Maximum
Operating Leased Assets [Line Items]
Operating leases, term	15 years
Other leased equipment and property | Maximum
Operating Leased Assets [Line Items]
Operating leases, term	25 years
Spare engines
Operating Leased Assets [Line Items]
Number of aircraft and spare engines financed under operating leases	10
Spare engines | Minimum
Operating Leased Assets [Line Items]
Operating leases, term	7 years
Spare engines | Maximum
Operating Leased Assets [Line Items]
Operating leases, term	12 years

Leases_and_Prepaid_Maintenance3

Leases and Prepaid Maintenance Deposits - Sale and Leaseback Transactions (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014
Sale Leaseback Transaction [Line Items]
Refund in pre-delivery deposits	$53.20
Spare engines
Sale Leaseback Transaction [Line Items]
Number of spare aircraft engines entered into sale and leaseback agreement	1
Quick Engine Change Kit
Sale Leaseback Transaction [Line Items]
Number of units under capital lease	2
Lease term	3 years
Aircraft
Sale Leaseback Transaction [Line Items]
Number of sale and leaseback transactions	31
Airbus A320
Sale Leaseback Transaction [Line Items]
Sale leaseback transaction, number of aircraft	8
Airbus A320 | Long-term assets
Sale Leaseback Transaction [Line Items]
Sale leaseback transaction on aircraft, net deferred gain (loss)	$1.60

Leases_and_Prepaid_Maintenance4

Leases and Prepaid Maintenance Deposits - Capital Leased Assets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Quick Engine Change Kit
Capital Leased Assets [Line Items]
Number of units under capital lease	2
Flight equipment
Capital Leased Assets [Line Items]
Flight equipment	$3,234	$3,234
Less: accumulated amortization	377	54
Capital leased assets, net	$2,857	$3,180

Leases_and_Prepaid_Maintenance5

Leases and Prepaid Maintenance Deposits - Future Minimum Lease Payments Under Noncancelable Operating Leases (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Future Minimum Lease Payments, Operating Leases
2015	$243,984
2016	237,751
2017	221,623
2018	198,082
2019	167,817
2020 and thereafter	663,987
Total minimum lease payments	1,733,244
Future Minimum Lease Payments, Capital Leases
2015	1,444
2016	1,044
2017	44
2018	44
2019	12
2020 and thereafter	0
Total minimum lease payments	2,588
Less amount representing interest	205
Present value of minimum lease payments	2,383	2,049
Less current portion	1,289
Long-term portion	1,094
Aircraft and Spare Engine Leases
Future Minimum Lease Payments, Operating Leases
2015	214,337
2016	212,512
2017	196,010
2018	172,323
2019	144,211
2020 and thereafter	592,409
Total minimum lease payments	1,531,802
Property Facility Leases
Future Minimum Lease Payments, Operating Leases
2015	29,647
2016	25,239
2017	25,613
2018	25,759
2019	23,606
2020 and thereafter	71,578
Total minimum lease payments	$201,442

Financial_Instruments_and_Risk2

Financial Instruments and Risk Management (Details) (USD $)	8 Months Ended	12 Months Ended			54 Months Ended	66 Months Ended
	Aug. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2014	Oct. 23, 2014
		aircraft				aircraft	derivative_instrument
		gal				gal
Derivative [Line Items]
Payments for premiums to acquire fuel options		$9,700,000
Into-plane fuel cost		608,033,000	542,523,000	471,542,000
Realized losses (gains)		995,000	8,958,000	175,000
Unrealized mark-to-market losses (gains)		3,881,000	265,000	46,000
Aircraft fuel		612,909,000	551,746,000	471,763,000
Underpayment of fuel, federal excise tax	2,100,000				9,300,000
Interest expense, past-due tax payments						800,000
Jet fuel consumption protected, fuel derivative (gallons)		88,700,000				88,700,000
Anticipated jet fuel consumption protected by hedges (percent)		35.00%				35.00%
Future aircraft to be received, next twelve months		15				15
Derivative instrument, change in fair value recorded within accumulated other comprehensive income, deferred tax		423,000	0	0
Interest rate swap
Derivative [Line Items]
Number of forward interest rate swaps							6
Derivative, notional amount							120,000,000
Interest rate swap, liability		1,100,000				1,100,000
Interest rate swap | Cash flow hedge
Derivative [Line Items]
Derivative instrument, change in fair value recorded within accumulated other comprehensive income		700,000
Derivative instrument, change in fair value recorded within accumulated other comprehensive income, deferred tax		$400,000
Airbus A321
Derivative [Line Items]
Number of aircraft protected by interest rate derivatives scheduled for delivery							3
Options held | Fuel
Derivative [Line Items]
Derivative, weighted-average ceiling price		2.07				2.07

Defined_Contribution_401k_Plan1

Defined Contribution 401(k) Plan (Details) (USD $)	12 Months Ended			0 Months Ended	5 Months Ended	7 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 01, 1994	Dec. 31, 2014	Jul. 31, 2014
	defined_contribution_plan
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, number of plans	3				3
Defined contribution 401(k) plan, matching contributions made in period	$9.70	$7.70	$6.60
Employee Retirement Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, requisite service period	60 days			1 year
Defined contribution 401(k) plan, requisite service period, hours				1000 hours
Defined contribution 401(k) plan, requisite age				21 years
Defined contribution plan, employer matching contribution, percent of match	50.00%
Employee Retirement Savings Plan | Maximum
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, maximum employer contribution percent of the employee’s annual compensation	3.00%
Pilots’ Retirement Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, requisite service period	60 days
Defined contribution 401(k) plan, requisite age	21 years
Defined contribution plan, employer matching contribution, percent of match					100.00%	100.00%
Pilots’ Retirement Savings Plan | Maximum
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, maximum employer contribution percent of the employee’s annual compensation					9.00%	8.00%
Puerto Rico Retirement Savings Plan | Pilots
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match					100.00%	100.00%
Puerto Rico Retirement Savings Plan | Other Employees
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match	50.00%
Puerto Rico Retirement Savings Plan | Maximum | Pilots
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, maximum employer contribution percent of the employee’s annual compensation					9.00%	8.00%
Puerto Rico Retirement Savings Plan | Maximum | Other Employees
Defined Contribution Plan Disclosure [Line Items]
Defined contribution 401(k) plan, maximum employer contribution percent of the employee’s annual compensation	3.00%

Income_Taxes_Components_of_the

Income Taxes - Components of the Provision for Income Taxes (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current:
Federal	$85,966	$86,437	$32,656
State and local	5,389	6,595	3,250
Foreign	2,057	413	963
Total current expense	93,412	93,445	36,869
Deferred:
Federal	34,240	11,658	27,870
State and local	-122	389	1,385
Total deferred expense (benefit)	34,118	12,047	29,255
Total income tax expense (benefit)	$127,530	$105,492	$66,124

Income_Taxes_Income_Tax_Reconc

Income Taxes - Income Tax Reconciliation (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Income Tax Expense
Expected provision at federal statutory tax rate	35.00%	35.00%	35.00%
State tax expense, net of federal benefit	1.00%	1.70%	2.10%
Income tax credits	-0.40%	0.00%	-0.10%
Other	0.50%	0.70%	0.90%
Total income tax expense (benefit)	36.10%	37.40%	37.90%

Income_Taxes_Deferred_Taxes_De

Income Taxes - Deferred Taxes (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred tax assets:
Net operating loss	$252	$188
Accrued rent	0	1,872
Deferred revenue	410	6,241
Nondeductible accruals	12,239	6,702
Deferred manufacturing credits	848	3,309
Unrealized gains/losses on derivatives	1,865	0
Accrued maintenance	3,073	1,225
Equity compensation	4,514	2,687
Other	661	16
Deferred tax assets	23,862	22,240
Deferred tax liabilities:
Capitalized interest	568	736
Deferred gain and losses on leases, net	2,349	1,882
Accrued rent	2,560	0
Prepaid expenses	1,681	0
Property, plant and equipment	37,369	6,384
Accrued engine maintenance	45,702	45,911
Deferred tax liabilities	90,229	54,913
Net deferred tax assets (liabilities)	-66,367	-32,673
Assets:
Current deferred tax assets, net	9,643	16,243
Liabilities:
Noncurrent deferred tax liabilities, net	$76,010	$48,916

Income_Taxes_Narrative_Details

Income Taxes - Narrative (Details) (USD $)	12 Months Ended			96 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012
Income Tax Disclosure [Abstract]
State net operating loss carryforwards	$2,700,000
Excess tax benefits from equity-based compensation	1,871,000	1,927,000	2,098,000
Foreign tax credit	1,200,000			1,400,000
Change in accounting principle, reduction of income tax payable	$35,000,000

Commitments_and_Contingencies_1

Commitments and Contingencies - Schedule of Future Aircraft Operating Leases (Details)	Dec. 31, 2014
	aircraft
Long-term Purchase Commitment [Line Items]
2015	15
2016	16
2017	18
2018	13
2019	13
2020	13
2021	18
Total future aircraft to be received	106
A320 | Airbus
Long-term Purchase Commitment [Line Items]
2015	8
2016	3
2017	8
2018	2
Total future aircraft to be received	21
A320NEO | Airbus
Long-term Purchase Commitment [Line Items]
2018	6
2019	3
2020	13
2021	18
Total future aircraft to be received	40
A320NEO | Third-Party Lessor
Long-term Purchase Commitment [Line Items]
2015	1
2016	4
Total future aircraft to be received	5
A321 | Airbus
Long-term Purchase Commitment [Line Items]
2015	6
2016	9
2017	10
2018	5
Total future aircraft to be received	30
A321NEO | Airbus
Long-term Purchase Commitment [Line Items]
2019	10
Total future aircraft to be received	10

Commitments_and_Contingencies_2

Commitments and Contingencies - Aircraft-Related Commitments and Financing Arrangements (Details) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified	aircraft
Airbus
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery	6
Number of aircraft without secured financing commitments scheduled for delivery	95
Number of aircraft with signed letters of intent, scheduled for delivery	5
Third-Party Lessor
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of direct leased aircraft ordered from a third party	5
Aircraft and Related Flight Equipment
Unrecorded Unconditional Purchase Obligation [Line Items]
Committed expenditures, 2015	660.1
Committed expenditures, 2016	604
Committed expenditures, 2017	763.4
Committed expenditures, 2018	621.4
Committed expenditures, 2019	711.1
Committed expenditures, 2020 and beyond	1,525.30
Reservation System and Advertising Media
Unrecorded Unconditional Purchase Obligation [Line Items]
Committed expenditures, 2015	5.1
Committed expenditures, 2016	3.9
Committed expenditures, 2017	3.9
Committed expenditures, 2018	2.6
Committed expenditures, 2019	0
Committed expenditures, 2020 and beyond	0
V2500 SelectOne Engine
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered	5
PurePower PW1100G-JM Engine
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered	9

Commitments_and_Contingencies_3

Commitments and Contingencies - Employees (Details) (USD $)	1 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Aug. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Jul. 08, 2014
			employee_group	employee
Concentration Risk [Line Items]
Union-represented employee groups		4	3
Number of airports in which company operates		56
Health Insurance Product Line
Concentration Risk [Line Items]
Accrued health care claims		3.1	2.1
Ramp Service Agents
Concentration Risk [Line Items]
Number of employees				250
International Association of Machinists and Aerospace Workers (IAM)
Concentration Risk [Line Items]
Number of airports in which company operates		4
Association of Flight Attendants (AFA-CWA)
Concentration Risk [Line Items]
Tentative collective bargaining agreement, contract term	5 years
Unionized employees concentration risk | Number of employees (percent)
Concentration Risk [Line Items]
Union-represented employee groups			3
Concentration of risk		67.00%	59.00%
Unionized employees concentration risk | Number of employees (percent) | International Association of Machinists and Aerospace Workers (IAM)
Concentration Risk [Line Items]
Concentration of risk		6.00%
Unionized employees concentration risk | Number of employees (percent) | Air Line Pilots Association, International (ALPA)
Concentration Risk [Line Items]
Concentration of risk		25.00%
Unionized employees concentration risk | Number of employees (percent) | Association of Flight Attendants (AFA-CWA)
Concentration Risk [Line Items]
Concentration of risk		35.00%
Unionized employees concentration risk | Number of employees (percent) | Transport Workers Union (TWU)
Concentration Risk [Line Items]
Concentration of risk		1.00%

Fair_Value_Measurements_Longte

Fair Value Measurements - Long-term Debt (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value	$148	$0
Senior loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value	132	0
Junior loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value	16	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value	148.1
Level 3 | Senior loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value	132
Level 3 | Junior loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value	$16.10

Fair_Value_Measurements_Assets

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (Recurring basis, USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$632.80	$530.60
Total assets	637.6	530.6
Total liabilities	1.1	0
Interest rate swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	1.1
Jet fuel options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Jet fuel options	4.8
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	632.8	530.6
Total assets	632.8	530.6
Total liabilities	0	0
Level 1 | Interest rate swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	0
Level 1 | Jet fuel options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Jet fuel options	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Total assets	0	0
Total liabilities	1.1	0
Level 2 | Interest rate swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	1.1
Level 2 | Jet fuel options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Jet fuel options	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Total assets	4.8	0
Total liabilities	0	0
Level 3 | Interest rate swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	0
Level 3 | Jet fuel options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Jet fuel options	$4.80

Fair_Value_Measurements_Assets1

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis using Significant Unobservable Inputs (Details) (Level 3, Jet fuel options, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Level 3 | Jet fuel options
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$0	$300,000	$300,000
Total realized or unrealized gains (losses) included in earnings, net	-4,900,000	100,000	-200,000
Purchases	9,700,000	0	0
Sales	0	0	0
Settlements, net	0	400,000	-200,000
Ending balance	$4,800,000	$0	$300,000

Operating_Segments_and_Related2

Operating Segments and Related Disclosures - Geographic Revenues (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenue	$474,487	$519,769	$499,337	$437,987	$419,984	$456,625	$407,339	$370,437	$1,931,580	$1,654,385	$1,318,388
DOT—domestic
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenue									1,728,800	1,467,500	1,135,100
DOT—Latin America
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenue									$202,800	$186,900	$183,300

Operating_Segments_and_Related3

Operating Segments and Related Disclosures - Foreign Revenues (Details) (Total passenger revenue, Any individual foreign country)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Total passenger revenue | Any individual foreign country
Concentration Risk [Line Items]
Concentration of risk (not greater than)	4.00%	4.00%	4.00%

Tax_Receivable_Agreement_Detai

Tax Receivable Agreement (Details) (USD $)	0 Months Ended		3 Months Ended	12 Months Ended
	Jun. 17, 2014	Mar. 31, 2011	Jun. 30, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 17, 2014	Jun. 01, 2011	Mar. 31, 2011
									owner
Tax Receivable Agreement [Abstract]
Percentage of cash savings from pre-IPO NOLs due to pre-IPO stockholders								90.00%
Tax receivable agreement, tax benefit schedule days to submission		45 days
Tax receivable agreement, number of largest owners pre initial public offering									2
Tax receivable agreement, tax benefit schedule days to response		45 days
Tax receivable agreement, tax benefit schedule days to resolve notice		30 days
Tax receivable agreement, tax benefit schedule days to payment after acceptance		5 days
Payments to pre-IPO shareholders pursuant to tax receivable agreement			($27,200,000)	($5,643,000)	$0	($26,905,000)
Interest included in cash payment to pre-IPO stockholders pursuant to tax receivable agreement			300,000
Estimated remaining cash payment to pre-IPO stockholders				0	5,643,000	8,000,000	5,600,000
Settlement amount	7,000,000
Settlement, interest expense	300,000
Excess tax payment resulting from settlement				$1,400,000

Quarterly_Financial_Data_Unaud2

Quarterly Financial Data (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Operating revenue	$474,487	$519,769	$499,337	$437,987	$419,984	$456,625	$407,339	$370,437	$1,931,580	$1,654,385	$1,318,388
Operating income	89,975	100,191	105,144	59,953	68,061	97,804	66,758	49,669	355,263	282,292	173,990
Net income	$55,909	$67,000	$64,849	$37,706	$43,193	$61,103	$42,068	$30,554	$225,464	$176,918	$108,460
Basic earnings per share (in dollars per share)	$0.77	$0.92	$0.89	$0.52	$0.59	$0.84	$0.58	$0.42	$3.10	$2.44	$1.50
Diluted earnings per share (in dollars per share)	$0.76	$0.91	$0.88	$0.51	$0.59	$0.84	$0.58	$0.42	$3.08	$2.42	$1.49