SkyWest (SKYW) 10-K 26 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 16, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	SKYWEST INC
Entity Central Index Key	793,733
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 1,816,989,866
Entity Common Stock, Shares Outstanding		51,784,012
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
CURRENT ASSETS:
Cash and cash equivalents	$ 181,792	$ 146,766
Marketable securities	503,503	409,898
Restricted cash		8,243
Income tax receivable	5,316	6,989
Receivables, net	42,731	46,916
Inventories, net	119,755	118,509
Prepaid aircraft rents	115,098	162,360
Other current assets	26,938	18,111
Total current assets	995,133	917,792
PROPERTY AND EQUIPMENT:
Aircraft and rotable spares	5,335,870	4,839,501
Deposits on aircraft	49,000	38,800
Buildings and ground equipment	265,608	261,704
Total property and equipment, gross	5,650,478	5,140,005
Less-accumulated depreciation and amortization	(1,467,475)	(1,318,308)
Total property and equipment, net	4,183,003	3,821,697
OTHER ASSETS
Long-term prepaid assets	230,923	218,505
Other long-term assets	49,220	49,972
Total other assets	280,143	268,477
Total assets	5,458,279	5,007,966
CURRENT LIABILITIES:
Current maturities of long-term debt	309,678	305,460
Accounts payable	288,904	241,215
Accrued salaries, wages and benefits	154,367	139,885
Taxes other than income taxes	19,228	15,618
Other current liabilities	48,648	45,087
Total current liabilities	820,825	747,265
OTHER LONG TERM LIABILITIES	42,541	50,844
LONG TERM DEBT, net of current maturities	2,377,346	2,240,051
DEFERRED INCOME TAXES PAYABLE	419,020	565,404
DEFERRED AIRCRAFT CREDITS	44,225	53,459
COMMITMENTS AND CONTINGENCIES (Note 5)
STOCKHOLDERS' EQUITY:
Preferred stock, 5,000,000 shares authorized; none issued
Common stock, no par value, 120,000,000 shares authorized; 80,398,104 and 79,781,305 shares issued, respectively	672,593	657,353
Retained earnings	1,516,957	1,103,751
Treasury stock, at cost, 28,643,535 and 28,015,386 shares, respectively	(435,178)	(410,090)
Accumulated other comprehensive loss	(50)	(71)
Total stockholders' equity	1,754,322	1,350,943
Total liabilities and stockholders' equity	$ 5,458,279	$ 5,007,966

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
CONSOLIDATED BALANCE SHEETS
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	80,398,104	79,781,305
Treasury stock, at cost, shares	28,643,535	28,015,386

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING REVENUES:
Passenger	$ 3,126,708	$ 3,051,414	$ 3,030,023
Ground handling and other	77,560	69,792	65,540
Total operating revenues	3,204,268	3,121,206	3,095,563
OPERATING EXPENSES:
Salaries, wages and benefits	1,196,227	1,211,380	1,203,312
Aircraft maintenance, materials and repairs	579,463	569,306	604,863
Depreciation and amortization	292,768	284,969	264,507
Aircraft rentals	215,807	262,602	273,696
Aircraft fuel	162,653	122,284	118,124
Ground handling services	69,848	72,659	82,694
Special items		465,649
Other operating expenses	299,303	305,041	313,852
Total operating expenses	2,816,069	3,293,890	2,861,048
OPERATING INCOME (LOSS)	388,199	(172,684)	234,515
OTHER INCOME (EXPENSE):
Interest income	4,509	2,143	1,997
Interest expense	(104,925)	(78,177)	(75,850)
Other, net	400	(94)	33,660
Total other expense, net	(100,016)	(76,128)	(40,193)
INCOME (LOSS) BEFORE INCOME TAXES	288,183	(248,812)	194,322
PROVISION (BENEFIT) FOR INCOME TAXES	(140,724)	(87,226)	76,505
NET INCOME (LOSS)	$ 428,907	$ (161,586)	$ 117,817
BASIC EARNINGS (LOSS) PER SHARE (in dollars per share)	$ 8.28	$ (3.14)	$ 2.31
DILUTED EARNINGS (LOSS) PER SHARE (in dollars per share)	$ 8.08	$ (3.14)	$ 2.27
Weighted average common shares:
Basic (in shares)	51,804	51,505	51,077
Diluted (in shares)	53,100	51,505	51,825
COMPREHENSIVE INCOME (LOSS):
Net income (loss)	$ 428,907	$ (161,586)	$ 117,817
Net unrealized appreciation on marketable securities, net of taxes	21	189	29
TOTAL COMPREHENSIVE INCOME (LOSS)	$ 428,928	$ (161,397)	$ 117,846

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Total
Balance at Dec. 31, 2014	$ 626,521	$ 1,165,478	$ (391,364)	$ (289)	$ 1,400,346
Balance (in shares) at Dec. 31, 2014	77,951		(26,765)
Increase (Decrease) in Stockholders' Equity
Net income (loss)		117,817			117,817
Net unrealized appreciation on marketable securities net of tax				29	29
Exercise of common stock options and vested restricted stock units	$ 8,490				8,490
Exercise of common stock options and vested restricted stock units (in shares)	815
Sale of common stock under employee stock purchase plan	$ 3,430				3,430
Sale of common stock under employee stock purchase plan (in shares)	254
Stock based compensation expense related to the issuance of stock options and restricted stock units	$ 5,368				5,368
Tax deficiency from exercise of common stock options	(2,166)				(2,166)
Treasury stock purchases			$ (18,726)		(18,726)
Treasury stock purchases (in shares)			(1,250)
Cash dividends declared (per share)		(8,153)			(8,153)
Balance at Dec. 31, 2015	$ 641,643	1,275,142	$ (410,090)	(260)	1,506,435
Balance (in shares) at Dec. 31, 2015	79,020		(28,015)
Increase (Decrease) in Stockholders' Equity
Net income (loss)		(161,586)			(161,586)
Net unrealized appreciation on marketable securities net of tax				189	189
Exercise of common stock options and vested restricted stock units	$ 4,979				4,979
Exercise of common stock options and vested restricted stock units (in shares)	609
Sale of common stock under employee stock purchase plan	$ 3,163				3,163
Sale of common stock under employee stock purchase plan (in shares)	152
Stock based compensation expense related to the issuance of stock options and restricted stock units	$ 7,568				7,568
Cash dividends declared (per share)		(9,805)			(9,805)
Balance at Dec. 31, 2016	$ 657,353	1,103,751	$ (410,090)	(71)	1,350,943
Balance (in shares) at Dec. 31, 2016	79,781		(28,015)
Increase (Decrease) in Stockholders' Equity
Net income (loss)		428,907			428,907
Net unrealized appreciation on marketable securities net of tax				21	21
Exercise of common stock options and vested restricted stock units	$ 1,658				1,658
Exercise of common stock options and vested restricted stock units (in shares)	529
Treasury shares withheld for the payment of taxes			$ (5,080)		(5,080)
Treasury shares withheld for the payment of taxes (in shares)			(145)
Sale of common stock under employee stock purchase plan (in shares)	88
Stock based compensation expense related to the issuance of stock options and restricted stock units	$ 3,002				3,002
Impact of adoption of Accounting Standards Update (ASU) 2016-09 (See Note 1)		867			867
Tax deficiency from exercise of common stock options	10,580				10,580
Treasury stock purchases			$ (20,008)		(20,008)
Treasury stock purchases (in shares)			(484)
Cash dividends declared (per share)		(16,568)			(16,568)
Balance at Dec. 31, 2017	$ 672,593	$ 1,516,957	$ (435,178)	$ (50)	$ 1,754,322
Balance (in shares) at Dec. 31, 2017	80,398		(28,644)

CONSOLIDATED STATEMENTS OF STO6

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY
Net unrealized depreciation on marketable securities, tax	$ 7	$ 98	$ 18
Cash dividends declared (in dollars per share)	$ 0.32	$ 0.19	$ 0.16

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 428,907	$ (161,586)	$ 117,817
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	292,768	284,969	264,507
Stock based compensation expense	10,580	7,568	5,368
Gain from early extinguishment of debt		(1,279)	(33,660)
Special items		465,649
Net increase (decrease) in deferred income taxes	(145,517)	(83,441)	73,844
Changes in operating assets and liabilities:
Decrease (increase) in restricted cash	8,243	(27)	3,366
Decrease in receivables	4,201	15,260	21,076
Decrease (increase) in income tax receivable	1,673	(4,118)	(92)
Increase in inventories	(1,246)	(1,986)	(2,860)
Decrease (increase) in other current assets	26,017	37,569	(28,598)
Decrease in deferred aircraft credits	(8,520)	(8,108)	(8,635)
Increase (decrease) in accounts payable and accrued aircraft rents	46,934	(47,563)	9,690
Increase (decrease) in other current liabilities	20,084	3,758	(4,498)
NET CASH PROVIDED BY OPERATING ACTIVITIES	684,124	506,665	417,325
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(1,533,867)	(2,511,388)	(1,170,439)
Sales of marketable securities	1,440,283	2,388,168	1,299,069
Proceeds from the sale of aircraft, property and equipment	51,994	3,008	10,308
Proceeds from settlement of residual value guarantee aircraft agreements		90,000
Acquisition of property and equipment:
Aircraft and rotable spare parts	(661,176)	(1,138,963)	(710,871)
Deposits on aircraft	(46,733)	(650)
Buildings and ground equipment	(27,467)	(14,350)	(10,405)
Return of deposits applied towards acquired aircraft	36,533		1,850
Decrease (increase) in other assets	(10,904)	7,097	10,772
NET CASH USED IN INVESTING ACTIVITIES	(751,337)	(1,177,078)	(569,716)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of long-term debt	471,677	926,069	591,881
Principal payments on long-term debt	(330,258)	(302,158)	(354,277)
Proceeds from issuance of common stock	4,660	8,142	9,754
Purchase of treasury stock	(20,008)		(18,726)
Employee income tax paid on equity awards	(5,080)
Decrease (increase) in debt issuance cost	(3,737)	(8,653)	2,779
Payment of cash dividends	(15,015)	(9,256)	(8,260)
NET CASH PROVIDED BY FINANCING ACTIVITIES	102,239	614,144	223,151
Increase (decrease) in cash and cash equivalents	35,026	(56,269)	70,760
Cash and cash equivalents at beginning of period	146,766	203,035	132,275
CASH AND CASH EQUIVALENTS AT END OF PERIOD	181,792	146,766	203,035
Non-cash investing activities:
Acquisition of rotable spare parts	755	5,688
Cash paid during the period for:
Interest, net of capitalized amounts	105,639	76,589	80,657
Income taxes	$ 5,010	$ 1,212	$ 5,104

Nature of Operations and Summar

Nature of Operations and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Nature of Operations and Summary of Significant Accounting Policies
Nature of Operations and Summary of Significant Accounting Policies	(1) Nature of Operations and Summary of Significant Accounting Policies SkyWest, Inc. (the “Company”), through its subsidiaries, SkyWest Airlines, Inc. (“SkyWest Airlines”) and ExpressJet Airlines, Inc. (“ExpressJet”), operates the largest regional airlines in the United States. As of December 31, 2017, SkyWest Airlines and ExpressJet offered scheduled passenger service under code-share agreements with United, Delta, American and Alaska with approximately 2,980 total daily departures to different destinations in the United States, Canada, Mexico and the Caribbean. Additionally, the Company provides airport customer service and ground handling services for other airlines throughout its system. As of December 31, 2017, the Company had 595 aircraft in scheduled service out of a combined fleet of 623 aircraft consisting of the following: CRJ200 CRJ700 CRJ900 ERJ135 ERJ145 E175 Total United 81 20 — 3 109 65 278 Delta 94 60 52 — — 19 225 American 16 49 — — — — 65 Alaska 4 — — — — 23 27 Aircraft in scheduled service 195 129 52 3 109 107 595 Subleased to an un-affiliated entity 4 — — — — — 4 Other* 9 7 — — 8 — 24 Total Fleet 208 136 52 3 117 107 623 * As of December 31, 2017, these aircraft have been removed from service and are in the process of being returned under the applicable leasing arrangement or are aircraft transitioning between code-share agreements with the Company’s major airline partners. During the year ended December 31, 2017, the Company sold eleven owned Embraer Brasilia EMB120 (“EMB120”) 30-seat turboprop aircraft at net book value. For the year ended December 31, 2017, approximately 46.7% of the Company’s aircraft in scheduled service operated for United, approximately 37.8% was operated for Delta, approximately 10.9% was operated for American and approximately 4.6% was operated for Alaska. SkyWest Airlines has been a code-share partner with Delta since 1987, United since 1997, Alaska since 2011 and American since 2012. As of December 31, 2017, SkyWest Airlines operated as a Delta Connection carrier primarily in Salt Lake City and Minneapolis, a United Express carrier primarily in Los Angeles, San Francisco, Denver, Houston, Chicago and the Pacific Northwest, an American carrier primarily in Chicago, Los Angeles and Phoenix and an Alaska carrier primarily in the Pacific Northwest. As of December 31, 2017, ExpressJet operated as a Delta Connection carrier primarily in Atlanta and Detroit, a United Express carrier primarily in Chicago (O’Hare), Cleveland, Newark and Houston and an American carrier primarily in Dallas. The Company’s subsidiaries operate the following aircraft manufactured by Bombardier Aerospace (“Bombardier”) and Embraer S.A. (“Embraer”): Bombardier CRJ200 regional jets (“CRJ200s”), Bombardier CRJ700 regional jets (“CRJ700s”), Bombardier CRJ900 regional jets (“CRJ900s”), Embraer ERJ145 Regional Jets (“ERJ145s”) and Embraer E175 dual-class regional jet aircraft (which are typically configured with 76 seats) (“E175s”). Additionally, the Company has ordered 30 E175 aircraft from Embraer configured with 70 seats (“E175 SC”). Basis of Presentation The Company’s consolidated financial statements include the accounts of the Company and the SkyWest Airlines, ExpressJet and SkyWest Leasing segments, with all inter‑company transactions and balances having been eliminated. In preparing the accompanying consolidated financial statements, the Company has reviewed, as determined necessary by the Company’s management, events that have occurred after December 31, 2017, through the filing date of the Company’s annual report with the U.S. Securities and Exchange Commission. The Company reclassified certain prior period amounts to conform to the current period presentation (see Recent Accounting Pronouncements). Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less to be cash equivalents. The Company classified $8.2 million of cash as restricted cash collateralizing letters of credit under the Company’s workers’ compensation insurance policy and classified it accordingly in the consolidated balance sheets as of December 31, 2016. The Company had no restricted cash as of December 31, 2017, as the Company satisfied the workers’ compensation insurance policy requirement with a letter of credit. Marketable Securities The Company’s investments in marketable debt and equity securities are deemed by management to be available-for-sale and are reported at fair market value with the net unrealized appreciation reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. At the time of sale, any realized appreciation or depreciation, calculated by the specific identification method, is recognized in other income and expense. The Company’s position in marketable securities as of December 31, 2017 and 2016 was as follows (in thousands): Gross unrealized Gross unrealized At December 31, 2017 Amortized Cost holding gains holding losses Fair market value Total cash and cash equivalents $ 181,792 $ — $ — $ 181,792 Marketable securities: Bond and bond funds $ 344,479 $ — $ (228) $ 344,251 Commercial Paper 159,252 — — 159,252 Total marketable securities $ 503,731 $ — $ (228) $ 503,503 Total assets measured at fair value $ 685,523 $ — $ (228) $ 685,295 Gross unrealized Gross unrealized At December 31, 2016 Amortized Cost holding gains holding losses Fair market value Total cash and cash equivalents $ 146,766 $ — $ — $ 146,766 Marketable securities: Bond and bond funds $ 410,001 $ — $ (116) $ 409,885 Commercial Paper 13 — — 13 Total marketable securities $ 410,014 $ — $ (116) $ 409,898 Total assets measured at fair value $ 556,780 $ — $ (116) $ 556,664 As of December 31, 2017 and 2016, the Company had classified $503.5 million and $409.9 million of marketable securities, respectively, as short‑term since it had the ability to redeem the securities within one year. Inventories Inventories include expendable parts, fuel and supplies and are valued at cost (FIFO basis) less an allowance for obsolescence based on historical results, excess parts and management’s expectations of future operations. Expendable inventory parts are charged to expense as used. An obsolescence allowance for flight equipment expendable parts is accrued based on estimated lives of the corresponding fleet types and salvage values. The inventory allowance as of December 31, 2017 and 2016 was $17.1 million and $40.5 million, respectively. The inventory allowance decreased in 2017 due to the disposal of excess inventory that had a valuation allowance as of December 31, 2016. These allowances are based on management estimates. Property and Equipment Property and equipment are stated at cost and depreciated over their useful lives to their estimated residual values using the straight‑line method. The Company changed the estimated useful lives and residual values for certain long-lived assets as of January 1, 2017 as follows: Assets Current Depreciable Life Prior Policy Depreciable Life Current Residual Value Prior Policy Residual Value New Aircraft 20 - 22 years 18 years 17.5 - 20 % % Used Aircraft, rotable spares, and spare engines up to 18 years up to 18 years 0 - 20 % 0 - 30 % Ground equipment up to 10 years No Change 0 % No Change Office equipment up to 7 years No Change % No Change Leasehold improvements Shorter of 15 years or lease term No Change % No Change Buildings 20 - 39.5 years No Change % No Change The impact of this change increased depreciation expense by an additional $1.4 million for 2017. Impairment of Long-Lived Assets As of December 31, 2017, the Company had approximately $4.2 billion of property and equipment and related assets. Additionally, as of December 31, 2017, the Company had approximately $4.9 million in intangible assets. In accounting for these long‑lived and intangible assets, the Company makes estimates about the expected useful lives of the assets, the expected residual values of certain of these assets, and the potential for impairment based on the fair value of the assets and the cash flows they generate. On September 7, 2005, the Company acquired all of the issued and outstanding capital stock of Atlantic Southeast and recorded an intangible asset for specifically identifiable contracts of approximately $33.7 million relating to the acquisition. The Company anticipates the intangible asset will be fully amortized by the end of 2018. As of December 31, 2017 and 2016, the Company had $28.9 million and $25.5 million in accumulated amortization expense, attributable to the acquisition, respectively. Factors indicating potential impairment include, but are not limited to, significant decreases in the market value of the long‑lived assets, a significant change in the condition of the long‑lived assets and operating cash flow losses associated with the use of the long‑lived assets. On a periodic basis, the Company evaluates whether impairment indicators are present. When considering whether or not impairment of long‑lived assets exists, the Company groups similar assets together at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities and compare the undiscounted cash flows for each asset group to the net carrying amount of the assets supporting the asset group. Asset groupings are done at the fleet or contract level. The Company did not recognize any impairment charges of long-lived assets during the year ended December 31, 2017. In 2016, the Company impaired certain long-lived assets relating to the CRJ200 aircraft and ERJ145 aircraft type specific assets. See Note 8, Special Items , for the impairment charges recorded during the year ended December 31, 2016. Capitalized Interest Interest is capitalized on aircraft purchase deposits as a portion of the cost of the asset and is depreciated over the estimated useful life of the asset. During the years ended December 31, 2017, 2016 and 2015, the Company capitalized interest costs of approximately $1.4 million, $1.5 million, and $2.2 million, respectively. Maintenance The Company operates under a U.S. Federal Aviation Administration approved continuous inspection and maintenance program. The Company uses the direct expense method of accounting for its regional jet engine overhauls wherein the expense is recorded when the overhaul event occurs. The Company has engine services agreements with third-party vendors to provide long-term engine services covering the scheduled and unscheduled repairs for certain of its CRJ200 aircraft, CRJ700 aircraft, ERJ145 aircraft and E175 aircraft. Under the terms of the agreements, the Company pays a fixed dollar amount per engine hour flown on a monthly basis and the third-party vendors will assume the responsibility to repair the engines at no additional cost to the Company, subject to certain specified exclusions. Maintenance costs under these contracts are recognized when the engine hour is flown pursuant to the terms of each contract. The costs of maintenance for airframe and avionics components, landing gear and other recurring maintenance are expensed as incurred. Passenger and Ground Handling Revenues The Company recognizes passenger and ground handling revenues when the service is provided under its code-share agreements. Under the Company’s fixed-fee arrangements (referred to as “fixed-fee arrangements, “fixed-fee contracts” or “capacity purchase agreements”) with Delta, United, American and Alaska (each, a “major airline partner”), the major airline partner generally pays the Company a fixed-fee for each departure, flight or block time incurred, and an amount per aircraft in service each month with additional incentives based on flight completion and on time performance. The major airline partner also directly reimburses the Company for certain direct expenses incurred under the fixed-fee arrangement such as fuel expense and certain airport related expenses. Under the fixed-fee arrangements, revenue is earned when each flight is completed. Under the Company’s fixed-fee agreements with Delta, United, American and Alaska, the compensation structure generally consists of a combination of agreed‑upon rates for operating flights and direct reimbursement for other certain costs associated with operating the aircraft. A portion of the Company’s contract flying compensation is designed to reimburse the Company for certain aircraft ownership costs. The aircraft compensation structure varies by agreement, but is intended to cover either the Company’s aircraft principal and interest debt service costs, its aircraft depreciation and interest expense or its aircraft lease expense costs while the aircraft is under contract. Under the Company’s ExpressJet United Express ERJ Agreement and certain aircraft operating under fixed-fee contracts with Delta, the major airline partner provides the aircraft to the Company for a nominal amount. The Company has concluded that a component of its revenue under these agreements is rental income, inasmuch as the agreements identify the “right of use” of a specific type and number of aircraft over a stated period of time. The amounts deemed to be rental income under the agreements for the years ended December 31, 2017, 2016 and 2015 were $572.7 million, $516.0 million and $504.9 million, respectively. These amounts are reflected as passenger revenues on the Company’s consolidated statements of comprehensive income (loss). The Company has not separately stated aircraft rental income and aircraft rental expense in the consolidated statement of comprehensive income (loss) since the use of the aircraft is not a separate activity of the total service provided. In the event that the contractual rates under the agreements have not been finalized at quarterly or annual financial statement dates, the Company records revenues based on the lower of prior period’s approved rates, as adjusted to reflect any contract negotiations and the Company’s estimate of rates that will be implemented in accordance with revenue recognition guidelines. In the event the Company has a reimbursement dispute with a major airline partner, the Company evaluates the dispute under its established revenue recognition criteria and, provided the revenue recognition criteria have been met, the Company recognizes revenue based on management’s estimate of the resolution of the dispute. In several of the Company’s agreements, the Company is eligible for incentive compensation upon the achievement of certain performance criteria. The incentives are defined in the agreements and are being measured and determined on a monthly, quarterly or semi-annual basis. At the end of each period, the Company calculates the incentives achieved during that period and recognizes revenue accordingly. The Company’s passenger revenues from fixed-fee agreements could be impacted by a number of factors, including changes to the Company’s code‑share agreements with Delta, United, Alaska or American, contract modifications resulting from contract re‑negotiations, the Company’s ability to earn incentive payments contemplated under the Company’s code‑share agreements and settlement of reimbursement disputes with the Company’s major airline partners. Under a Revenue Sharing Arrangement (referred to as a “revenue-sharing” or “prorate” arrangement), the major airline and regional airline negotiate a passenger fare proration formula, pursuant to which the regional airline receives a percentage of the ticket revenues for those passengers traveling for one portion of their trip on the regional airline and the other portion of their trip on the major airline. Revenue is recognized under the Company’s prorate flying agreements when each flight is completed based upon the portion of the prorate passenger fare the Company anticipates that it will receive for each completed flight. Other ancillary revenues commonly associated with airlines such as baggage fee revenue, ticket change fee revenue and the marketing component of the sale of mileage credits are retained by the Company’s major airline partners on flights that the Company operates under its code-share agreements. The following summarizes the significant provisions of each code-share agreement the Company has with each major airline partner: Delta Connection Agreements Agreement Aircraft type Number of Aircraft Term / Termination SkyWest Airlines Delta Connection Agreement (fixed-fee arrangement)  CRJ 200  CRJ 700  CRJ 900  E175 70 27 36 19  Individual aircraft have scheduled removal dates under the agreement between 2018 and 2027  The average remaining term of the aircraft under contract is 2.9 years ExpressJet Delta Connection Agreement (fixed-fee arrangement)  CRJ 700  CRJ 900 33 16  Individual aircraft have scheduled removal dates under the agreement during 2018 SkyWest Airlines Delta Connection Prorate Agreement (revenue-sharing arrangement)  CRJ 200 24  Terminable with 30-day notice United Express Agreements Agreement Aircraft type Number of Aircraft Term / Termination SkyWest Airlines United Express Agreements (fixed-fee arrangement)  CRJ 200  CRJ 700  E175 57 20 65  Individual aircraft have scheduled removal dates under the agreement between 2018 and 2029  The average remaining term of the aircraft under contract is 5.1 years ExpressJet United ERJ Agreement (fixed-fee arrangement)  ERJ145  ERJ135 109 3  Agreement expires in 2022  The average remaining term of the aircraft under contract is 4.8 years SkyWest Airlines United Express Prorate Agreement (revenue-sharing arrangement)  CRJ 200 24  Terminable with 120-day notice American Agreements Agreement Aircraft type Number of Aircraft Term / Termination Dates SkyWest Airlines American Agreement (fixed-fee arrangement)  CRJ 200  CRJ 700 10 37  CRJ200 aircraft are scheduled to expire in 2018 and the CRJ700 aircraft are scheduled to expire in 2019 SkyWest Airlines American Prorate Agreement (revenue-sharing arrangement)  CRJ 200 6  Terminable with 120-day notice ExpressJet American Agreement (fixed-fee arrangement)  CRJ 700 12  CRJ700 aircraft are scheduled to expire in 2019 Alaska Capacity Purchase Agreement Agreement Aircraft type Number of Aircraft Term / Termination SkyWest Airlines Alaska Agreement (fixed-fee arrangement)  CRJ 200  E175 4 23  CRJ200 aircraft are scheduled to expire in 2018  E175 aircraft have scheduled removal dates under the agreement between 2027 and 2029 In addition to the contractual arrangements described above, SkyWest Airlines has entered into agreements with Alaska and Delta to place additional E175/E175 SC aircraft into service for those major airline partners. As of December 31, 2017, the Company anticipated placing an additional 12 E175 aircraft with Alaska and 30 E175 SC aircraft with Delta. The delivery dates for the new E175/E175 SC aircraft are currently scheduled to take place by the end of 2018 or early 2019. Final delivery dates may adjust based on various factors. ExpressJet initiated the wind down of its flying agreement with Delta during 2017 and expected to be complete by the end of 2018. As of December 31, 2017, ExpressJet operated 49 CRJ700s/900s under its Delta flying agreement. Of the 49 aircraft, ExpressJet anticipates returning 19 leased aircraft to Delta and removing 30 CRJ700 aircraft from service with Delta during 2018. ExpressJet is pursuing placement of the 30 CRJ700 aircraft with other partners, of which eight aircraft are scheduled to be placed under an agreement with American following the removal from service with Delta. Deferred Aircraft Credits The Company accounts for incentives provided by aircraft manufacturers as deferred credits. The deferred credits related to leased aircraft are amortized on a straight‑line basis as a reduction to rent expense over the lease term. Credits related to owned aircraft reduce the purchase price of the aircraft, which has the effect of amortizing the credits on a straight‑line basis as a reduction in depreciation expense over the life of the related aircraft. The incentives are credits that may be used to purchase spare parts and pay for training and other expenses. Income Taxes The Company recognizes a net liability or asset for the deferred tax consequences of all temporary differences between the tax basis of assets and liabilities and their reported amounts in the consolidated financial statements that are expected to result in taxable or deductible amounts in future years when the reported amounts of the assets and liabilities are recovered or settled. Net Income (Loss) Per Common Share Basic net income (loss) per common share (“Basic EPS”) excludes dilution and is computed by dividing net income (loss) by the weighted average number of common shares outstanding during the period. Diluted net income (loss) per common share (“Diluted EPS”) reflects the potential dilution that could occur if stock options or other contracts to issue common stock were exercised or converted into common stock. The computation of Diluted EPS does not assume exercise or conversion of securities that would have an anti‑dilutive effect on net income (loss) per common share. During the year ended December 31, 2017, 284,000 performance shares (at target performance) were excluded in the computation of Diluted EPS since the Company had not achieved the minimum target thresholds as of December 31, 2017. During the year ended December 31, 2016, 2,077,000 shares reserved for the issuance upon the exercise of outstanding options, performance shares and restricted stock units were excluded from the computation of Diluted EPS due to the net loss in 2016 and 505,000 shares reserved for outstanding options were excluded from the Diluted EPS calculation for the year ended December 31, 2015 as the respective exercise price exceeded the weighted average fair market value of the Company’s stock for 2015. The calculation of the weighted average number of common shares outstanding for Basic EPS and Diluted EPS are as follows for the years ended December 31, 2017, 2016 and 2015 (in thousands): Year Ended December 31, 2017 2016 2015 Numerator: Net Income (Loss) $ 428,907 $ (161,586) $ 117,817 Denominator: Denominator for basic earnings per-share weighted average shares 51,804 51,505 51,077 Dilution due to stock options and restricted stock units 1,296 — 748 Denominator for diluted earnings per-share weighted average shares 53,100 51,505 51,825 Basic earnings (loss) per-share $ 8.28 $ (3.14) $ 2.31 Diluted earnings (loss) per-share $ 8.08 $ (3.14) $ 2.27 Comprehensive Income (Loss) Comprehensive income (loss) includes charges and credits to stockholders’ equity that are not the result of transactions with the Company’s shareholders, including changes in unrealized appreciation on marketable securities. Fair Value of Financial Instruments The carrying amounts reported in the consolidated balance sheets for receivables and accounts payable approximate fair values because of the immediate or short‑term maturity of these financial instruments. Marketable securities are reported at fair value based on market quoted prices in the consolidated balance sheets. If quoted prices in active markets are no longer available, the Company has estimated the fair values of these securities utilizing a discounted cash flow analysis as of December 31, 2017. These analyses consider, among other items, the collateralization underlying the security investments, the creditworthiness of the counterparty, the timing of expected future cash flows, and the expectation of the next time the security is expected to have a successful auction. The fair value of the Company’s long‑term debt is estimated based on current rates offered to the Company for similar debt and was approximately $2,698.4 million as of December 31, 2017, as compared to the carrying amount of $2,712.4 million as of December 31, 2017. The Company’s fair value of long‑term debt as of December 31, 2016 was $2,566.5 million as compared to the carrying amount of $2,570.9 million as of December 31, 2016. Segment Reporting Generally accepted accounting principles require disclosures related to components of a company for which separate financial information is available to, and regularly evaluated by, the Company’s chief operating decision maker when deciding how to allocate resources and in assessing performance. The Company’s three operating segments consist of the operations conducted by SkyWest Airlines, ExpressJet and SkyWest Leasing. Information pertaining to the Company’s reportable segments is presented in Note 2, Segment Reporting . Recent Accounting Pronouncements Standards Effective in Future Years and Not Yet Adopted In May 2014, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update No. 2014‑09, “Revenue from Contracts with Customers” (“ASU No. 2014‑09”). Under ASU No. 2014‑09, revenue is recognized at the time a good or service is transferred to a customer for the amount of consideration received for that specific good or service. In 2016, the FASB issued several amendments to the standard, including principal versus agent considerations when another party is involved in providing goods or services to a customer and the application of identifying performance obligations. The Company’s adoption of the standard as of January 1, 2018, will be first presented in the first quarter of 2018, utilizing the full retrospective method of adoption allowed by the standard, in order to provide for comparative results in all periods presented. Under the new standard, the Company concluded that individual flights are distinct services and these flight services promised in a CPA agreement represent a series of services that should be accounted for as a single performance obligation, recognized over time as the flights are completed. The adoption of ASU No. 2014‑09 did not have a material impact on recorded amounts when applied to the opening balance sheet as of January 1, 2018 and is not expected to impact the amount or timing of the future amounts of net income, however the principal versus agent considerations under ASU No. 2014-09 will result in the Company recording directly reimbursed fuel expense under its fixed-fee contracts as a reduction to the applicable operating expense (net) rather than revenue (gross). The Company’s analysis of information necessary to recast prior period results is still preliminary and additional impacts could still result when the standard is first applied to revenue transactions during the first quarter of 2018. In February 2016, the FASB issued Accounting Standards Update 2016‑02, “Leases (Topic 842)” (“ASU No. 2016-02”). ASU No. 2016‑02 amends the existing accounting standards for lease accounting, including requiring lessees to recognize most leases on their balance sheets and making targeted changes to lessor accounting. ASU No. 2016‑02 will be effective beginning in the first quarter of 2019. Early adoption of ASU No. 2016‑02 is permitted. ASU No. 2016‑02 requires a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application, with an option to use certain transition relief. The Company’s management is currently evaluating the impact the adoption of ASU 2016‑02 is anticipated to have on the Company’s consolidated financial statements. In 2016, the FASB issued Accounting Standards Update 2016‑15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” and Accounting Standard Update 2016‑18, “Statement of Cash Flows (Topic 230): Restricted Cash” related to the classification of certain cash receipts and cash payments and the presentation of restricted cash within an entity’s statement of cash flows, respectively. These standards are effective for interim and annual reporting periods beginning after December 15, 2017, but early adoption is permitted. The Company anticipates adopting this standard in the first quarter of 2018 that will modify the presentation of changes in restricted cash in the Company’s Consolidated Statement of Cash Flows. Recently Adopted Standards Pursuant to the guidelines of the recently issued Accounting Standards Update 2015-17, “Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes” (“ASU 2015‑17”), all net deferred tax assets and liabilities are to be classified as non-current. As permitted under ASU 2015‑17, the Company adopted this guidance for the quarter ended March 31, 2017. The Company adopted ASU 2015‑17 retrospectively. Upon adoption, approximately $129.3 million of formerly recorded current deferred tax assets as of December 31, 2016 were reclassified to non-current and netted against non-current deferred income taxes payable as of December 31, 2016 in the accompanying financial statements. In March 2016, the FASB issued Accounting Standards Update No. 2016‑09, “Compensation—Stock Compensation (Topic 718)” (“ASU No. 2016‑09”). ASU No. 2016‑09 makes several amendments to Topic 718, which simplified the accounting for share-based payment transactions, including the income tax consequences, the calculation of diluted earnings per share, the treatment of forfeitures and the classification on the statement of cash flows. Amendments related to the timing of when excess tax benefits are recognized, minimum statutory withholding requirements and forfeitures should be applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity as of the beginning of the period in which the guidance is adopted. Amendments requiring the recognition of excess tax benefits and tax deficiencies in the income statement should be applied prospectively. Prior to the adoption of ASU No. 2016‑09, accounting principles generally accepted in the United States of America (“GAAP”) required tax effects of deductions for share-based payments in excess of compensation cost and tax deficiencies to be recorded in equity. Under ASU No. 2016‑09, the tax effects of awards are treated as discrete income tax expense items in the reporting period in which they occur. The Company adopted ASU No. 2016‑09 as of January 1, 2017. The adoption of this standard resulted in the recognition in of $0.9 million of previously unrecognized excess tax benefits in net deferred tax liabilities and an increase to retained earnings on the consolidated balance sheet as of the beginning of the current year, and the recognition of $5.4 million of excess tax benefits in the income tax provision for the year ended December 31, 2017. The adoption of ASU No. 2016‑09 did not have a material impact on the statement of cash flows presentation.

Segment Reporting

Segment Reporting	12 Months Ended
	Dec. 31, 2017
Segment Reporting
Segment Reporting	(2) Segment Reporting Generally accepted accounting principles require disclosures related to components of a company for which separate financial information is available to, and regularly evaluated by, the Company’s chief operating decision maker when deciding how to allocate resources and in assessing performance. The Company’s three reporting segments consist of the operations of SkyWest Airlines, ExpressJet and SkyWest Leasing activities. Corporate overhead expenses incurred by the Company are allocated to the operating expenses of SkyWest Airlines and ExpressJet. The Company’s chief operating decision maker analyzes the profitability of operating the E175 aircraft (including operating costs and associated revenue) separately from the profitability of the Company’s ownership, financing costs and associated revenue of the Company’s E175 aircraft (including depreciation expense, interest expense and associated revenue). The SkyWest Leasing segment includes revenue attributed to the Company’s E175 aircraft ownership cost earned under the applicable fixed-fee contracts and the depreciation and interest expense of the Company’s E175 aircraft. The SkyWest Leasing segment’s total assets and capital expenditures include the acquired E175 aircraft. The SkyWest Leasing segment additionally includes the activity of four CRJ200 aircraft leased to a third-party. The following represents the Company’s segment data for the years ended December 31, 2017, 2016 and 2015 (in thousands). Year Ended December 31, 2017 SkyWest Airlines ExpressJet SkyWest Leasing Consolidated Operating revenues $ 2,173,384 $ 790,942 $ 239,942 $ 3,204,268 Operating expense 1,888,556 819,343 108,170 2,816,069 Depreciation and amortization expense 134,563 51,982 106,223 292,768 Interest expense 21,544 4,127 79,254 104,925 Segment profit (loss) (1) 263,284 (32,528) 52,518 283,274 Identifiable intangible assets, other than goodwill — 4,896 — 4,896 Total assets 2,228,930 599,122 2,630,227 5,458,279 Capital expenditures (including non-cash) 124,955 14,278 550,165 689,398 Year Ended December 31, 2016 SkyWest Airlines ExpressJet SkyWest Leasing Consolidated Operating revenues $ 1,935,378 $ 1,044,828 $ 141,000 $ 3,121,206 Operating expense 1,886,173 1,339,569 68,148 3,293,890 Depreciation and amortization expense 139,159 83,935 61,875 284,969 Special items 184,295 281,354 — 465,649 Interest expense 26,211 6,773 45,193 78,177 Segment profit (loss) (1) 22,994 (301,514) 27,659 (250,861) Identifiable intangible assets, other than goodwill — 8,249 — 8,249 Total assets 2,250,276 582,890 2,174,800 5,007,966 Capital expenditures (including non-cash) 57,761 15,396 1,085,844 1,159,001 Year Ended December 31, 2015 SkyWest Airlines ExpressJet SkyWest Leasing Consolidated Operating revenues $ $ $ $ 3,095,563 Operating expense 38,778 2,861,048 Depreciation and amortization expense 264,507 Interest expense 75,850 Segment profit (loss) (1) 182,022 (34,238) 10,881 158,665 Identifiable intangible assets, other than goodwill — — 10,499 Total assets 4,781,984 Capital expenditures (including non-cash) 715,089 (1) Segment profit is operating income less interest expense

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2017
Long-Term Debt
Long-Term Debt	(3) Long‑term Debt Long‑term debt consisted of the following as of December 31, 2017 and 2016 (in thousands): December 31, December 31, 2017 2016 Notes payable to banks, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.91% to 3.43% through 2020, secured by aircraft $ 34,905 $ Notes payable to a financing company, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.85% to 3.25% through 2021, secured by aircraft 97,612 Notes payable to banks, due in semi-annual installments plus interest at 6.06% to 6.51% through 2021, secured by aircraft 63,090 Notes payable to a financing company, due in semi-annual installments plus interest at 5.78% to 6.23% through 2017, secured by aircraft — Notes payable to banks, due in monthly installments plus interest of 2.68% to 6.86% through 2025, secured by aircraft 372,157 Notes payable to banks, due in monthly installments, plus interest at 4.16% to 6.05% through 2029, secured by aircraft 49,001 Notes payable to banks, due in monthly installments, plus interest at 3.44% through 2019, secured by aircraft — Notes payable to banks, due in quarterly installments, plus interest at 3.39% to 4.73% through 2029, secured by aircraft 2,085,822 Notes payable to banks, due in monthly installments, plus interest based on LIBOR at 3.54% through 2017, secured by aircraft — Notes payable to banks due in monthly installments, interest at 3.30% through 2019, secured by spare engines 9,763 Long-term debt $ 2,712,350 $ Current portion of long-term debt (313,243) (308,945) Less long-term portion of unamortized debt issue cost, net (21,761) (21,908) Long-term debt, net of current maturities and debt issue costs $ 2,377,346 $ 2,240,051 Current portion of long-term debt 313,243 308,945 Less current portion of unamortized debt issue cost, net (3,565) (3,485) Current portion of long-term debt, net of debt issue costs $ 309,678 $ 305,460 During the year ended December 31, 2017, the Company acquired 21 new E175 aircraft. Approximately 85% of the aircraft purchase price was financed through the issuance of debt and 15% of the aircraft purchase price was paid with cash. As of December 31, 2017 and 2016, the Company had $2.7 billion and $2.6 billion, respectively, of long‑term debt obligations primarily related to the acquisition of aircraft and certain spare engines. The average effective interest rate on the debt related to those long-term debt obligations at December 31, 2017 and 2016, was approximately 3.9% and 3.8%, respectively. During the year ended December 31, 2016, the Company used $16.5 million in cash to extinguish $18.4 million in debt early. The payment resulted in a pre-tax gain of $1.3 million, reflected as other income in the consolidated statements of comprehensive income (loss). During the year ended December 31, 2015, the Company used $110.8 million in cash to pay off $145.4 million in debt. The payment resulted in a pre-tax gain of $33.7 million, reflected as other income in the consolidated statements of comprehensive income (loss). The Company did not extinguish any debt early during 2017. The aggregate amounts of principal maturities of long‑term debt as of December 31, 2017 were as follows (in thousands): 2018 $ 313,243 2019 2020 2021 2022 Thereafter $ 2,712,350 As of December 31, 2017 and 2016, SkyWest Airlines had a $75 million line of credit. The line of credit includes minimum liquidity and profitability covenants and is secured by certain assets. As of December 31, 2017 and 2016, SkyWest Airlines had no amount outstanding under the facility. However, at December 31, 2017 and 2016 the Company had $14.8 million and $6.5 million, respectively, in letters of credit issued under the facility which reduced the amount available under the facility to $60.2 million and $68.5 million, respectively. The facility expires on June 1, 2018 and has a variable interest rate of LIBOR plus 2.5% (4.1% at December 31, 2017). As of December 31, 2017 and 2016, the Company had $87.4 million and $87.7 million, respectively, in letters of credit and surety bonds outstanding with various banks and surety institutions.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Taxes
Income Taxes	(4) Income Taxes The provision (benefit) for income taxes includes the following components (in thousands): Year ended December 31, 2017 2016 2015 Current tax provision (benefit): Federal $ 5,853 $ (3,801) $ 3,801 State 180 111 1,035 6,033 (3,690) 4,836 Deferred tax provision (benefit): Federal (166,890) (77,430) 66,430 State 20,133 (6,106) 5,239 (146,757) (83,536) 71,669 Provision (benefit) for income taxes $ (140,724) $ (87,226) $ 76,505 The following is a reconciliation between a federal income tax rate of 35% of income (loss) before income taxes and the effective tax rate which is derived by dividing the provision (benefit) for income taxes by income (loss) before for income taxes (in thousands): Year ended December 31, 2017 2016 2015 Computed provision (benefit) for income taxes at the statutory rate $ 100,864 $ (87,084) $ 68,013 Increase (decrease) in income taxes resulting from: State income tax provision (benefit), net of federal income tax benefit 7,778 (5,768) 5,416 Non-deductible expenses 3,230 3,552 3,641 Valuation allowance changes affecting the provision for income taxes 505 751 (899) Excess tax benefits from share-based compensation (5,377) — — Revaluation of net deferred taxes for the Tax Act (246,845) — — Other, net (879) 1,323 334 Provision (benefit) for income taxes $ (140,724) $ (87,226) $ 76,505 On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Tax Act”) was enacted. The Tax Act makes broad and complex changes to the U.S. tax code that may affect our income tax accounting at December 31, 2017 and future periods, including, but not limited to reducing the U.S. federal corporate tax rate from the previous rate of 35% to 21% , requiring companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred, and creates new taxes on certain foreign sourced earnings. The SEC staff issued Staff Accounting Bulletin 118 (“SAB 118”), which provides guidance on accounting for the tax effects of the Tax Act. SAB 118 provides a measurement period that should not extend beyond one year from the Tax Act enactment date for companies to complete the accounting under Accounting Standards Codification 740 (“ASC 740”). In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Tax Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the Tax Act. In connection with our initial analysis of the impact of the Tax Act and consistent with the requirement to record a provisional estimate when applicable, the Company made a reasonable estimate of the effects of the Tax Act and recorded a discrete net income tax benefit at December 31, 2017 of approximately $246.8 million. This provisional estimate primarily consists of a net benefit for the corporate rate reduction due to the revaluing of the Company’s net deferred tax liabilities, including certain state related effects, as a result of the reduction in the federal corporate tax rates. The Company made certain estimates in evaluating the Tax Act impact on state income taxes and other deferred tax items. The Company is continuing to gather information and analyze aspects of the Tax Act, which could potentially affect the estimated impact on the deferred tax balances. These estimates may be affected as the Company gains a more thorough understanding of the Tax Act, including the deductibility of purchased assets, state tax treatment, and amounts related to employee compensation. The impact of the Tax Act may differ from our estimates, possibly materially, due to, among other things, changes in interpretations and assumptions the Company has made, guidance that may be issued and actions the Company may take as a result of the Tax Act. The Company will continue to update the provisional estimates as information is obtained, such as state impacts regarding decoupling from the Tax Act provisions, realization of deferred amounts, and accounting method elections that may be made by the Company. For the years ended December 31, 2017, 2016 and 2015 the Company recorded a $0.5 million, $0.8 million and $0.9 million valuation allowance, respectively against certain deferred tax assets primarily associated with ExpressJet state net operating losses with a limited carry forward period. The increase of the valuation allowance was based on changes in state tax laws and the Company's income tax projections which increased the amount of deferred tax assets that are anticipated to expire before the deferred tax assets may be utilized. The Company recorded a $5.4 million benefit from share-based compensation in 2017 relating to ASU 2016-09 which, beginning in 2017, requires excess tax benefits and deficiencies to be recognized in the income tax provision during the period stock options are exercised and when stock awards vest. The significant components of the Company’s net deferred tax assets and liabilities as of December 31, 2017 and 2016 are as follows (in thousands): As of December 31, 2017 2016 Deferred tax assets: Intangible asset $ (206) $ 4,983 Accrued benefits 31,651 48,482 Net operating loss carryforward 122,648 286,389 AMT credit carryforward 23,443 17,589 Deferred aircraft credits 53,870 60,415 Accrued reserves and other 26,853 47,906 Total deferred tax assets 258,259 465,764 Valuation allowance (10,642) (8,877) Deferred tax liabilities: Accelerated depreciation (666,637) (1,022,291) Total deferred tax liabilities (666,637) (1,022,291) Net deferred tax liability $ (419,020) $ (565,404) The Company’s deferred tax liabilities were primarily generated through accelerated depreciation, combined with shorter depreciable tax lives, allowed under the IRS tax code for purchased aircraft and support equipment compared to the Company’s depreciation policy under GAAP for such assets using the straight-line method (see note 1 Nature of Operations and Summary of Significant Accounting Policies). The Company's valuation allowance is related to certain deferred tax assets with a limited carry forward period where the Company does not anticipate utilizing these deferred tax assets prior to the lapse of the carry forward period. At December 31, 2017 and 2016, the Company had federal net operating losses of approximately $491.4 million and $763.9 million and state net operating losses of approximately $302.5 million and $469.2 million, respectively. The estimated effective tax rate applicable to the federal and state net operating losses at December 31, 2017 was 21.0% and 3.36%, respectively. The Company anticipated that the federal and state net operating losses will start to expire in 2034 and 2018, respectively. The Company has recorded a valuation allowance for state net operating losses the Company anticipates will expire before the benefit will be realized due to the limited carry forward periods. As of December 31, 2017 and 2016, the Company also had an alternative minimum tax credit of approximately $23.4 million and $17.6 million, respectively, which does not expire. Under the new the Tax Act, the alternative minimum tax credit is anticipated to be realized by the Company either by offsetting regular tax due or as a refundable credit over the next four years .

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies
Commitments and Contingencies	(5) Commitments and Contingencies Lease Obligations The Company leases 319 aircraft, as well as airport facilities, office space, and various other property and equipment under non‑cancelable operating leases which are generally on a long‑term net rent basis where the Company pays taxes, maintenance, insurance and certain other operating expenses applicable to the leased property. The following table summarizes future minimum rental payments required under operating leases that have non‑cancelable lease terms as of December 31, 2017 (in thousands): 2018 $ 142,157 2019 104,297 2020 121,119 2021 112,657 2022 75,981 Thereafter 160,621 $ 716,832 The majority of the Company’s leased aircraft are owned and leased through trusts whose sole purpose is to purchase, finance and lease these aircraft to the Company (“Leveraged Lease Agreements”); therefore, they meet the criteria of a variable interest entity. However, since these are single owner trusts in which the Company does not participate, the Company is not considered at risk for losses and is not considered the primary beneficiary. As a result, the Company has not consolidated any of these trusts or any other entities in applying the accounting guidance. The Company’s management believes that the Company’s maximum exposure under these leases is the remaining lease payments. Total rental expense for non-cancelable aircraft operating leases was approximately $215.8 million, $262.6 million and $273.7 million for the years ended December 31, 2017, 2016 and 2015, respectively. The minimum rental expense for airport station rents was approximately $30.3 million, $31.4 million and $35.1 million for the years ended December 31, 2017, 2016 and 2015, respectively. Self‑insurance The Company self‑insures a portion of its potential losses from claims related to workers’ compensation, environmental issues, property damage, medical insurance for employees and general liability. Losses are accrued based on an estimate of the ultimate aggregate liability for claims incurred, using standard industry practices and the Company’s actual experience. Actual results could differ from these estimates. Legal Matters The Company is subject to certain legal actions which it considers routine to its business activities. As of December 31, 2017, management believed, after consultation with legal counsel, that the ultimate outcome of such legal matters was not likely to have a material adverse effect on the Company’s financial position, liquidity or results of operations. Concentration Risk and Significant Customers The Company requires no collateral from its major airline partners or customers, but monitors the financial condition of its major airline partners. Under the majority of the Company’s code-share agreements, the Company receives weekly payments from its major code-share partners that approximate a significant percentage of the compensation earned for such period. Additionally, the Company provides certain customer service functions at multiple airports for various airlines and the Company maintains an allowance for doubtful accounts receivable based upon expected collectability of all accounts receivable. The Company’s allowance for doubtful accounts totaled $157,000 and $173,000 as of December 31, 2017 and 2016, respectively. For the years ended December 31, 2017, 2016 and 2015, the Company’s contractual relationships with Delta and United combined accounted for approximately 78.8%, 85.4% and 86.9%, respectively of the Company’s total revenues. Employees Under Collective Bargaining Agreements As of December 31, 2017, the Company had approximately 16,300 full‑time equivalent employees. Approximately 22.0% of these employees were represented by unions, including the following employee groups. Notwithstanding the completion of the ExpressJet Combination, ExpressJet’s employee groups continue to be represented by those unions who provided representation prior to the ExpressJet Combination. Accordingly, the following table refers to ExpressJet’s employee groups based upon their union affiliations prior to the ExpressJet Combination. Approximate Number of Active Employees Status of Employee Group Represented Representatives Agreement Atlantic Southeast Pilots Air Line Pilots Association International Amendable February 2018 Atlantic Southeast Flight Attendants International Association of Machinists and Aerospace Workers Currently Amendable Atlantic Southeast Flight Controllers Transport Workers Union of America Currently Amendable Atlantic Southeast Mechanics International Brotherhood of Teamsters Currently Amendable Atlantic Southeast Stock Clerks International Brotherhood of Teamsters Currently Amendable ExpressJet Delaware Pilots Air Line Pilots Association International Amendable February 2018 ExpressJet Delaware Flight Attendants International Association of Machinists and Aerospace Workers Currently Amendable ExpressJet Delaware Mechanics International Brotherhood of Teamsters Amendable January 2019 ExpressJet Delaware Dispatchers Transport Workers Union of America Currently Amendable ExpressJet Delaware Stock Clerks International Brotherhood of Teamsters Currently Amendable In January 2018, the ExpressJet Delaware Mechanics ratified a one-year contract extension to their labor agreement.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Measurements
Fair Value Measurements	(6) Fair Value Measurements The Company holds certain assets that are required to be measured at fair value in accordance with GAAP. The Company determined fair value of these assets based on the following three levels of inputs: 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. Some of the Company’s marketable securities primarily utilize broker quotes in a non‑active market for valuation of these securities. 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, therefore requiring an entity to develop its own assumptions. As of December 31, 2017, the Company held certain assets that are required to be measured at fair value on a recurring basis. Assets measured at fair value on a recurring basis are summarized below (in thousands): Fair Value Measurements as of December 31, 2017 Total Level 1 Level 2 Level 3 Marketable Securities Bonds and bond funds $ $ — $ $ — Commercial paper — — $ $ — $ $ — Cash, Cash Equivalents and Restricted Cash — — Total Assets Measured at Fair Value $ $ $ $ — Fair Value Measurements as of December 31, 2016 Total Level 1 Level 2 Level 3 Marketable Securities Bonds and bond funds $ $ — $ $ — Commercial paper — 13 — $ $ — $ $ — Cash, Cash Equivalents and Restricted Cash — — Total Assets Measured at Fair Value $ $ $ $ — The Company’s “Marketable Securities” classified as Level 2 primarily utilize broker quotes in a non‑active market for valuation of these securities. No significant transfers between Level 1, Level 2 and Level 3 occurred during the year ended December 31, 2017. The Company’s policy regarding the recording of transfers between levels is to record any such transfers at the end of the reporting period.

Investment in Other Companies

Investment in Other Companies	12 Months Ended
	Dec. 31, 2017
Investment in Other Companies
Investment in Other Companies	(7) Investment in Other Companies In 2014, the Company completed the sale of its 20% interest in Brazilian airline, TRIP Linhas Aéreas (“TRIP”), to TRIP Investments Ltd. (“TRIP Investimentos”). As part of the sale transaction, the Company also received options to acquire a minority interest in TRIP Investimentos. The options have an initial exercise price per share equal to the price paid by TRIP Investimentos to acquire TRIP shares from the Company subject to annual escalations. The options are scheduled to expire in 2018. The options were recorded as an asset at a nominal amount in 2014.

Special Items

Special Items	12 Months Ended
	Dec. 31, 2017
Special Items
Special Items	(8) Special Items The following table summarizes the components of the Company's special items, for the year ended December 31, 2017, 2016 and 2015 (in thousands): Year ended December 31, 2017 2016 2015 Special items: CRJ200 aircraft related items 1 $ — $ 424,466 $ — ERJ145 aircraft related items 2 — 41,183 — Total special items $ — $ 465,649 $ — (1) Consists primarily of inventory valuation charges and impairment charges to write-down CRJ200 aircraft including related long-lived assets to their estimated fair value. The estimated fair value of the long-lived assets, including the aircraft and fixed asset spare parts inventory, was based on third-party appraisals on the assets. These values were estimated based on listed market values or recent third-party market transactions for similar assets. Additionally, the Company estimated the fair value of certain long-lived prepaid lease assets using the net present value of estimated current CRJ200 lease rates. All fair values are considered to be Level 3 within the fair value hierarchy. Of the special items $184.3 million related to SkyWest Airlines and $240.2 million related to ExpressJet. These charges are net of $90 million in cash proceeds and other considerations from the Bombardier termination agreement. These special items are reflected in the SkyWest Airlines and ExpressJet operating expenses under Note 2 Segment Reporting. (2) The ERJ145 aircraft related items recorded in the 2016 special charge consist primarily of inventory valuation charges and impairment charges to write-down certain ERJ145 long-lived assets, which primarily consisted of spare engines and ERJ145 spare aircraft parts, to their estimated fair value of $41.2 million. The estimated fair value of the long-lived assets was based on third-party appraisals and valuations for similar assets which is considered an unobservable input (Level 3) under the fair value hierarchy. These special items are reflected in the ExpressJet operating expenses under Note 2 Segment Reporting .

Capital Transactions

Capital Transactions	12 Months Ended
	Dec. 31, 2017
Capital Transactions
Capital Transactions	(9) Capital Transactions Preferred Stock The Company is authorized to issue 5,000,000 shares of preferred stock in one or more series without shareholder approval. No shares of preferred stock are presently outstanding. The Company’s Board of Directors is authorized, without any further action by the shareholders of the Company, to (i) divide the preferred stock into series; (ii) designate each such series; (iii) fix and determine dividend rights; (iv) determine the price, terms and conditions on which shares of preferred stock may be redeemed; (v) determine the amount payable to holders of preferred stock in the event of voluntary or involuntary liquidation; (vi) determine any sinking fund provisions; and (vii) establish any conversion privileges. Stock Compensation On May 4, 2010, the Company’s shareholders approved the adoption of the SkyWest, Inc. 2010 Long‑Term Incentive Plan, which provides for the issuance of up to 5,150,000 shares of common stock to the Company’s directors, employees, consultants and advisors (the “2010 Incentive Plan”). The 2010 Incentive Plan provides for awards in the form of options to acquire shares of common stock, stock appreciation rights, restricted stock grants, restricted stock units and performance awards. The 2010 Incentive Plan is administered by the Compensation Committee of the Company’s Board of Directors (the “Compensation Committee”), which is authorized to designate option grants as either incentive stock options for income tax purposes (“ISO”) or non-statutory stock options ISOs are granted at not less than 100% of the market value of the underlying common stock on the date of grant. Non‑statutory stock options are granted at a price as determined by the Compensation Committee. Stock Options The fair value of stock options awarded under the Company’s stock option plans has been estimated as of the grant date using the Black‑Scholes option pricing model. The Company uses historical data to estimate option exercises and employee termination in the option pricing model. The expected term of options granted is derived from the output of the option pricing model and represents the period of time that options granted are expected to be outstanding. The expected volatilities are based on the historical volatility of the Company’s traded stock and other factors. During the year ended December 31, 2017, the Company did not grant any options to purchase shares of common stock. The Company granted 206,021 and 267,433 stock options to employees under the 2010 Incentive Plan during the years ended December 31, 2016 and 2015, respectively. Stock options granted in 2015 and 2016 vest in three equal installments over a three-year period. The following table shows the assumptions used and weighted average fair value for grants in the years ended December 31, 2016 and 2015. 2016 2015 Expected annual dividend rate 1.08 % 1.18 % Risk-free interest rate 1.15 % 1.62 % Average expected life (years) 5.7 5.7 Expected volatility of common stock 0.412 0.401 Forfeiture rate % % Weighted average fair value of option grants $ 5.27 $ 4.75 The Company recorded share‑based compensation expense only for those options that are expected to vest. The estimated fair value of the stock options is amortized over the vesting period of the respective stock option grants. Options are exercisable for a period as defined by the Compensation Committee on the date granted; however, no stock option will be exercisable before six months have elapsed from the date of grant and no stock option shall be exercisable after seven years from the date of grant. The following table summarizes the stock option activity for all of the Company’s plans for the years ended December 31, 2017, 2016 and 2015: 2017 2016 2015 Weighted Weighted Average Aggregate Weighted Weighted Average Remaining Intrinsic Average Average Number of Exercise Contractual Value Number of Exercise Number of Exercise Options Price Term ($000) Options Price Options Price Outstanding at beginning of year 819,981 $ 13.58 4.4 years $ 18,756.9 1,064,429 $ 13.64 2,888,074 $ 16.46 Granted — — 206,021 14.90 267,433 Exercised (356,209) 13.36 (351,296) 14.17 (544,917) Cancelled (5,669) 14.33 (99,173) 14.90 (1,546,161) Outstanding at end of year 458,103 13.73 4.0 years $ 18,034.1 819,981 13.58 1,064,429 Exercisable at December 31, 2017 254,192 13.17 3.4 years $ 10,150.8 Exercisable at December 31, 2016 263,851 13.76 2.8 years $ 5,985.5 The total intrinsic value of options to acquire shares of the Company’s common stock that were exercised during the years ended December 31, 2017, 2016 and 2015 was $9,940,000, $4,250,000 and $1,800,000, respectively. The following table summarizes the status of the Company’s non‑vested stock options as of December 31, 2017: Weighted-Average Number of Grant-Date Shares Fair Value Non-vested shares at beginning of year 556,130 $ 4.86 Granted — — Vested (346,550) 4.67 Cancelled (5,669) 5.14 Non-vested shares at end of year $ 5.17 The following table summarizes information about the Company’s stock options outstanding at December 31, 2017: Options Outstanding Options Exercisable Weighted Average Number Remaining Weighted Average Number Weighted Average Range of Exercise Prices Outstanding Contractual Life Exercise Price Exercisable Exercise Price $8.00 to $12.99 3.1 years $ 12.06 $ $13.00 to $14.99 4.2 years $15.00 to $19.00 4.8 years $8.00 to $19.00 4.0 years $ $ Restricted Stock Units During the year ended December 31, 2017, the Company granted 160,137 restricted stock units to certain of the Company’s employees under the 2010 Incentive Plan. The restricted stock units granted during the year ended December 31, 2017 have a three‑year cliff-vesting period, during which the recipient must remain employed with the Company or its subsidiaries. The weighted average fair value of the restricted stock units at the date of grants made during the year ended December 31, 2017 was $35.81 per share. The following table summarizes the activity of restricted stock units granted to certain Company employees for the years ended December 31, 2017, 2016 and 2015: During the year ended December 31, 2016, the Company granted 380,358 shares of restricted stock units to certain Company’s employees under the 2010 Incentive Plan. The restricted stock units granted during the year ended December 31, 2016 have a three‑year vesting period, during which the recipient must remain employed with the Company or its subsidiaries. The weighted average fair value of the restricted stock units the date of grants made during the year ended December 31, 2016 was $14.81 per share. The following table summarizes the activity of restricted stock units granted to certain Company employees as of December 31, 2016, 2015 and 2014: Weighted-Average Grant-Date Fair Number of Shares Value Non-vested shares outstanding at December 31, 2014 723,176 $ 12.70 Granted 408,163 13.57 Vested (215,856) 13.06 Cancelled (106,184) 13.52 Non-vested shares outstanding at December 31, 2015 809,299 $ 13.13 Granted 384,148 14.81 Vested (215,146) 13.29 Cancelled (51,370) 13.72 Non-vested shares outstanding at December 31, 2016 926,931 $ 13.65 Granted 160,137 35.81 Vested (230,903) 12.01 Cancelled (40,575) 15.78 Non-vested shares outstanding at December 31, 2017 815,590 $ 18.35 Performance Stock Units During the year ended December 31, 2017, the Compensation Committee granted performance share units, which are performance based restricted stock units, to certain Company employees with three-year performance-based financial metrics that the Company must meet before those awards may be earned and the performance period is measured for the three years ending December 31, 2019. The Compensation Committee will determine the achievement of performance results and corresponding vesting of performance shares for each year’s grant in 2015, 2016 and 2017. At the end of each performance period, the number of shares awarded can range from 0% to 200% of the original granted amount for performance share units granted in 2017 and can range from 0% to 150% of the original granted amount for performance shares granted in 2015 and 2016, depending on the performance against the pre-established targets. The following table summarizes the activity of performance share units granted at target as of December 31, 2017. Weighted-Average Grant-Date Fair Number of Shares Value Non-vested shares outstanding at December 31, 2014 — $ — Granted 13.61 Vested — — Cancelled (19,754) 13.51 Non-vested shares outstanding at December 31, 2015 202,829 $ 13.62 Granted 14.89 Vested — — Cancelled (22,413) 14.16 Non-vested shares outstanding at December 31, 2016 363,993 $ 14.23 Granted 35.81 Vested — — Cancelled (14,732) 15.00 Non-vested shares outstanding at December 31, 2017 $ 19.70 During the years ended December 31, 2017, 2016 and 2015 the Company granted fully‑vested shares of common stock to the Company’s directors in the amounts of 22,617, 42,624 and 36,950 shares, respectively, with a weighted average grant‑date fair value of $35.81, $14.78, and $14.05, respectively. During the year ended December 31, 2017, 2016 and 2015, the Company recorded equity‑based compensation expense of $10.6 million, $7.6 million and $5.4 million, respectively. As of December 31, 2017, the Company had $10.6 million of total unrecognized compensation cost related to non‑vested stock options, non‑vested restricted stock grants and non-vested performance stock units. Total unrecognized compensation cost will be adjusted for future changes in estimated forfeitures. The Company expects to recognize this cost over a weighted average period of 1.7 years. Taxes The Company’s treatment of stock option grants of non‑qualified options, restricted stock units and performance shares results in the creation of a deferred tax asset, which is a temporary difference, until the time that the option is exercised or the restrictions lapse.

Retirement Plans and Employee S

Retirement Plans and Employee Stock Purchase Plans	12 Months Ended
	Dec. 31, 2017
Retirement Plans and Employee Stock Purchase Plans
Retirement Plans and Employee Stock Purchase Plans	(10) Retirement Plans and Employee Stock Purchase Plans SkyWest Retirement Plan The Company sponsors the SkyWest, Inc. Employees’ Retirement Plan (the “SkyWest Plan”). Employees who have completed 90 days of service and are at least 18 years of age are eligible for participation in the SkyWest Plan. Employees may elect to make contributions to the SkyWest Plan. Generally, the Company matches 100% of such contributions up to levels ranging from 2% to 7% of compensation, based on position and years of service. Additionally, a discretionary contribution may be made by the Company. The Company’s combined contributions to the SkyWest Plan were $26.1 million, $23.2 million and $20.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. ExpressJet and Atlantic Southeast Retirement Plans ExpressJet (formerly Atlantic Southeast) sponsors the Atlantic Southeast Airlines, Inc. Investment Savings Plan (the “Atlantic Southeast Plan”). Employees who have completed 90 days of service and are 18 years of age are eligible for participation in the Atlantic Southeast Plan. Employees may elect to make contributions to the Atlantic Southeast Plan, ExpressJet will match up to 8% of each participant’s total compensation, based on years of service and other provisions included in the Atlantic Southeast Plan. Additionally, participants are 100% vested in their elective deferrals and rollover amounts and from 10% to 100% vested in company matching contributions based on length of service. ExpressJet additionally sponsors the ExpressJet Airlines, Inc. 401(k) Savings Plan (the “ExpressJet Retirement Plan”). Substantially all of ExpressJet’s domestic employees were covered by this plan at the time the Company acquired ExpressJet in 2010. Effective January 1, 2009, the ExpressJet Retirement Plan was amended such that certain matching payment amounts have been reduced or eliminated depending on the terms of the collective bargaining unit or work group, as applicable. ExpressJet’s contribution to the Atlantic Southeast and the ExpressJet Retirement Plans was $17.8 million, $21.0 million and $24.0 million for the years ended December 31, 2017, 2016 and 2015, respectively. Employee Stock Purchase Plans In May 2009, the Company’s Board of Directors approved the SkyWest, Inc. 2009 Employee Stock Purchase Plan (the “2009 Stock Purchase Plan”). All employees who have completed 90 days of employment with the Company or one of its subsidiaries are eligible to participate in the 2009 Stock Purchase Plan, except employees who own five percent or more of the Company’s common stock. The 2009 Stock Purchase Plan enables employees to purchase shares of the Company’s common stock at a five percent discount, through payroll deductions. Employees can contribute up to 15% of their base pay, not to exceed $25,000 each calendar year, for the purchase of shares. Shares are purchased semi-annually at a five percent discount based on the end of the period price. Employees can terminate their participation in the 2009 Stock Purchase Plan at any time upon written notice. The following table summarizes purchases made under the 2009 Employee Stock Purchase Plans during the years ended December 31, 2017, 2016 and 2015: Year ended December 31, 2017 2016 2015 Number of shares purchased 88,362 151,531 254,098 Average price of shares purchased $ 33.96 $ 20.87 $ 13.50 The 2009 Stock Purchase Plan is a non‑compensatory plan under the accounting guidance. Therefore, no compensation expense was recorded for the years ended December 31, 2017, 2016 and 2015.

Stock Repurchase

Stock Repurchase	12 Months Ended
	Dec. 31, 2017
Stock Repurchase
Stock Repurchase	(11) Stock Repurchase The Company’s Board of Directors has adopted a stock repurchase program which authorizes the Company to repurchase shares of the Company’s common stock in the public market or in private transactions, from time to time, at prevailing prices. The Company’s stock repurchase program authorizes the repurchase of up to $100.0 million of the Company’s common stock, over a three year period commencing on February 9, 2017, of which $80.0 million remained available at December 31, 2017. During the years ended December 31, 2017 and 2015, the Company repurchased 0.5 million and 1.3 million shares of common stock for approximately $20.0 million and $18.7 million, respectively at a weighted average price per share of $41.36 and $14.98, respectively. The Company did not repurchase any shares of its common stock during the year ended December 31, 2016. Additionally, during the year ended December 31, 2017, the Company paid $5.1 million for a net settlement of the income tax obligation on employee equity awards.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2017
Related-Party Transactions
Related-Party Transactions	(12) Related‑Party Transactions During the year ended December 31, 2017, the Company purchased $198,000 of spare aircraft parts from an entity affiliated with a director of the Company.

Quarterly Financial Data (Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data (Unaudited)
Quarterly Financial Data (Unaudited)	(13) Quarterly Financial Data (Unaudited) Unaudited summarized financial data by quarter for 2017 and 2016 is as follows (in thousands, except per share data): Year ended December 31, 2017 First Second Third Fourth Quarter Quarter Quarter Quarter Year Operating revenues $ 765,415 $ 809,759 $ 831,936 $ 797,158 $ Operating income 76,295 106,596 112,369 92,939 388,199 Net income(1) 34,786 50,477 53,716 289,928 428,907 Net income per common share: Basic 5.60 8.28 Diluted 5.46 8.08 Weighted average common shares: Basic: 51,820 51,751 51,833 51,811 51,804 Diluted: 53,202 52,977 53,080 53,140 53,100 Year ended December 31, 2016 First Second Third Fourth Quarter Quarter Quarter Quarter Year Operating revenues $ 762,075 $ 801,338 $ 799,776 $ $ Operating income (loss) 61,809 84,137 85,834 (172,684) Net income (loss)(2) 27,092 40,244 41,322 (161,586) Net income (loss) per common share: Basic Diluted Weighted average common shares: Basic: 51,218 51,418 51,627 Diluted: 52,014 52,194 52,471 (1) Net income for 2017 included a $246.8 million benefit related to the revaluation of the Company’s deferred tax liability and other tax liabilities in accordance with the Tax Act. (2) Operating loss for the fourth quarter of 2016 included a special charge of $465.6 million related to an impairment on the Company’s 50-seat aircraft.

SCHEDULE II_VALUATION AND QUALI

SCHEDULE II—VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2017
SCHEDULE II—VALUATION AND QUALIFYING ACCOUNTS
SCHEDULE II—VALUATION AND QUALIFYING ACCOUNTS	SKYWEST, INC. AND SUBSIDIARIES SCHEDULE II—VALUATION AND QUALIFYING ACCOUNTS For the Years Ended December 31, 2017, 2016 and 2015 (Dollars in thousands) Additions Balance at Charged to Beginning Costs and Balance at Description of Year Expenses Deductions End of Year Year ended December 31, 2017: Allowance for inventory obsolescence(1) $ 40,497 — (23,399) $ 17,098 Allowance for doubtful accounts receivable 173 — (16) 157 $ 40,670 — (23,415) $ 17,255 Year ended December 31, 2016: Allowance for inventory obsolescence(2) $ 13,933 26,564 — $ 40,497 Allowance for doubtful accounts receivable 187 — (14) 173 $ 14,120 26,564 (14) $ 40,670 Year ended December 31, 2015: Allowance for inventory obsolescence $ 11,588 2,345 — $ 13,933 Allowance for doubtful accounts receivable 326 — (139) 187 $ 11,914 2,345 (139) $ 14,120 (1) The deductions in 2017 related to the disposal of excess and obsolete inventory in 2017. (2) The increase in the inventory obsolescence related to additional excess inventory identified as part of the impairment analysis of the 50-seat aircraft. See note 8, Special items , for additional detail on the impairment.

Nature of Operations and Summ22

Nature of Operations and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Nature of Operations and Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The Company’s consolidated financial statements include the accounts of the Company and the SkyWest Airlines, ExpressJet and SkyWest Leasing segments, with all inter‑company transactions and balances having been eliminated. In preparing the accompanying consolidated financial statements, the Company has reviewed, as determined necessary by the Company’s management, events that have occurred after December 31, 2017, through the filing date of the Company’s annual report with the U.S. Securities and Exchange Commission. The Company reclassified certain prior period amounts to conform to the current period presentation (see Recent Accounting Pronouncements).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less to be cash equivalents. The Company classified $8.2 million of cash as restricted cash collateralizing letters of credit under the Company’s workers’ compensation insurance policy and classified it accordingly in the consolidated balance sheets as of December 31, 2016. The Company had no restricted cash as of December 31, 2017, as the Company satisfied the workers’ compensation insurance policy requirement with a letter of credit.
Marketable Securities	Marketable Securities The Company’s investments in marketable debt and equity securities are deemed by management to be available-for-sale and are reported at fair market value with the net unrealized appreciation reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. At the time of sale, any realized appreciation or depreciation, calculated by the specific identification method, is recognized in other income and expense. The Company’s position in marketable securities as of December 31, 2017 and 2016 was as follows (in thousands): Gross unrealized Gross unrealized At December 31, 2017 Amortized Cost holding gains holding losses Fair market value Total cash and cash equivalents $ 181,792 $ — $ — $ 181,792 Marketable securities: Bond and bond funds $ 344,479 $ — $ (228) $ 344,251 Commercial Paper 159,252 — — 159,252 Total marketable securities $ 503,731 $ — $ (228) $ 503,503 Total assets measured at fair value $ 685,523 $ — $ (228) $ 685,295 Gross unrealized Gross unrealized At December 31, 2016 Amortized Cost holding gains holding losses Fair market value Total cash and cash equivalents $ 146,766 $ — $ — $ 146,766 Marketable securities: Bond and bond funds $ 410,001 $ — $ (116) $ 409,885 Commercial Paper 13 — — 13 Total marketable securities $ 410,014 $ — $ (116) $ 409,898 Total assets measured at fair value $ 556,780 $ — $ (116) $ 556,664 As of December 31, 2017 and 2016, the Company had classified $503.5 million and $409.9 million of marketable securities, respectively, as short‑term since it had the ability to redeem the securities within one year.
Inventories	Inventories Inventories include expendable parts, fuel and supplies and are valued at cost (FIFO basis) less an allowance for obsolescence based on historical results, excess parts and management’s expectations of future operations. Expendable inventory parts are charged to expense as used. An obsolescence allowance for flight equipment expendable parts is accrued based on estimated lives of the corresponding fleet types and salvage values. The inventory allowance as of December 31, 2017 and 2016 was $17.1 million and $40.5 million, respectively. The inventory allowance decreased in 2017 due to the disposal of excess inventory that had a valuation allowance as of December 31, 2016. These allowances are based on management estimates.
Property and Equipment	Property and Equipment Property and equipment are stated at cost and depreciated over their useful lives to their estimated residual values using the straight‑line method. The Company changed the estimated useful lives and residual values for certain long-lived assets as of January 1, 2017 as follows: Assets Current Depreciable Life Prior Policy Depreciable Life Current Residual Value Prior Policy Residual Value New Aircraft 20 - 22 years 18 years 17.5 - 20 % % Used Aircraft, rotable spares, and spare engines up to 18 years up to 18 years 0 - 20 % 0 - 30 % Ground equipment up to 10 years No Change 0 % No Change Office equipment up to 7 years No Change % No Change Leasehold improvements Shorter of 15 years or lease term No Change % No Change Buildings 20 - 39.5 years No Change % No Change
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets As of December 31, 2017, the Company had approximately $4.2 billion of property and equipment and related assets. Additionally, as of December 31, 2017, the Company had approximately $4.9 million in intangible assets. In accounting for these long‑lived and intangible assets, the Company makes estimates about the expected useful lives of the assets, the expected residual values of certain of these assets, and the potential for impairment based on the fair value of the assets and the cash flows they generate. On September 7, 2005, the Company acquired all of the issued and outstanding capital stock of Atlantic Southeast and recorded an intangible asset for specifically identifiable contracts of approximately $33.7 million relating to the acquisition. The Company anticipates the intangible asset will be fully amortized by the end of 2018. As of December 31, 2017 and 2016, the Company had $28.9 million and $25.5 million in accumulated amortization expense, attributable to the acquisition, respectively. Factors indicating potential impairment include, but are not limited to, significant decreases in the market value of the long‑lived assets, a significant change in the condition of the long‑lived assets and operating cash flow losses associated with the use of the long‑lived assets. On a periodic basis, the Company evaluates whether impairment indicators are present. When considering whether or not impairment of long‑lived assets exists, the Company groups similar assets together at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities and compare the undiscounted cash flows for each asset group to the net carrying amount of the assets supporting the asset group. Asset groupings are done at the fleet or contract level. The Company did not recognize any impairment charges of long-lived assets during the year ended December 31, 2017. In 2016, the Company impaired certain long-lived assets relating to the CRJ200 aircraft and ERJ145 aircraft type specific assets. See Note 8, Special Items , for the impairment charges recorded during the year ended December 31, 2016.
Capitalized Interest	Capitalized Interest Interest is capitalized on aircraft purchase deposits as a portion of the cost of the asset and is depreciated over the estimated useful life of the asset. During the years ended December 31, 2017, 2016 and 2015, the Company capitalized interest costs of approximately $1.4 million, $1.5 million, and $2.2 million, respectively.
Maintenance	Maintenance The Company operates under a U.S. Federal Aviation Administration approved continuous inspection and maintenance program. The Company uses the direct expense method of accounting for its regional jet engine overhauls wherein the expense is recorded when the overhaul event occurs. The Company has engine services agreements with third-party vendors to provide long-term engine services covering the scheduled and unscheduled repairs for certain of its CRJ200 aircraft, CRJ700 aircraft, ERJ145 aircraft and E175 aircraft. Under the terms of the agreements, the Company pays a fixed dollar amount per engine hour flown on a monthly basis and the third-party vendors will assume the responsibility to repair the engines at no additional cost to the Company, subject to certain specified exclusions. Maintenance costs under these contracts are recognized when the engine hour is flown pursuant to the terms of each contract. The costs of maintenance for airframe and avionics components, landing gear and other recurring maintenance are expensed as incurred.
Passenger and Ground Handling Revenues	Passenger and Ground Handling Revenues The Company recognizes passenger and ground handling revenues when the service is provided under its code-share agreements. Under the Company’s fixed-fee arrangements (referred to as “fixed-fee arrangements, “fixed-fee contracts” or “capacity purchase agreements”) with Delta, United, American and Alaska (each, a “major airline partner”), the major airline partner generally pays the Company a fixed-fee for each departure, flight or block time incurred, and an amount per aircraft in service each month with additional incentives based on flight completion and on time performance. The major airline partner also directly reimburses the Company for certain direct expenses incurred under the fixed-fee arrangement such as fuel expense and certain airport related expenses. Under the fixed-fee arrangements, revenue is earned when each flight is completed. Under the Company’s fixed-fee agreements with Delta, United, American and Alaska, the compensation structure generally consists of a combination of agreed‑upon rates for operating flights and direct reimbursement for other certain costs associated with operating the aircraft. A portion of the Company’s contract flying compensation is designed to reimburse the Company for certain aircraft ownership costs. The aircraft compensation structure varies by agreement, but is intended to cover either the Company’s aircraft principal and interest debt service costs, its aircraft depreciation and interest expense or its aircraft lease expense costs while the aircraft is under contract. Under the Company’s ExpressJet United Express ERJ Agreement and certain aircraft operating under fixed-fee contracts with Delta, the major airline partner provides the aircraft to the Company for a nominal amount. The Company has concluded that a component of its revenue under these agreements is rental income, inasmuch as the agreements identify the “right of use” of a specific type and number of aircraft over a stated period of time. The amounts deemed to be rental income under the agreements for the years ended December 31, 2017, 2016 and 2015 were $572.7 million, $516.0 million and $504.9 million, respectively. These amounts are reflected as passenger revenues on the Company’s consolidated statements of comprehensive income (loss). The Company has not separately stated aircraft rental income and aircraft rental expense in the consolidated statement of comprehensive income (loss) since the use of the aircraft is not a separate activity of the total service provided. In the event that the contractual rates under the agreements have not been finalized at quarterly or annual financial statement dates, the Company records revenues based on the lower of prior period’s approved rates, as adjusted to reflect any contract negotiations and the Company’s estimate of rates that will be implemented in accordance with revenue recognition guidelines. In the event the Company has a reimbursement dispute with a major airline partner, the Company evaluates the dispute under its established revenue recognition criteria and, provided the revenue recognition criteria have been met, the Company recognizes revenue based on management’s estimate of the resolution of the dispute. In several of the Company’s agreements, the Company is eligible for incentive compensation upon the achievement of certain performance criteria. The incentives are defined in the agreements and are being measured and determined on a monthly, quarterly or semi-annual basis. At the end of each period, the Company calculates the incentives achieved during that period and recognizes revenue accordingly. The Company’s passenger revenues from fixed-fee agreements could be impacted by a number of factors, including changes to the Company’s code‑share agreements with Delta, United, Alaska or American, contract modifications resulting from contract re‑negotiations, the Company’s ability to earn incentive payments contemplated under the Company’s code‑share agreements and settlement of reimbursement disputes with the Company’s major airline partners. Under a Revenue Sharing Arrangement (referred to as a “revenue-sharing” or “prorate” arrangement), the major airline and regional airline negotiate a passenger fare proration formula, pursuant to which the regional airline receives a percentage of the ticket revenues for those passengers traveling for one portion of their trip on the regional airline and the other portion of their trip on the major airline. Revenue is recognized under the Company’s prorate flying agreements when each flight is completed based upon the portion of the prorate passenger fare the Company anticipates that it will receive for each completed flight. Other ancillary revenues commonly associated with airlines such as baggage fee revenue, ticket change fee revenue and the marketing component of the sale of mileage credits are retained by the Company’s major airline partners on flights that the Company operates under its code-share agreements. The following summarizes the significant provisions of each code-share agreement the Company has with each major airline partner: Delta Connection Agreements Agreement Aircraft type Number of Aircraft Term / Termination SkyWest Airlines Delta Connection Agreement (fixed-fee arrangement)  CRJ 200  CRJ 700  CRJ 900  E175 70 27 36 19  Individual aircraft have scheduled removal dates under the agreement between 2018 and 2027  The average remaining term of the aircraft under contract is 2.9 years ExpressJet Delta Connection Agreement (fixed-fee arrangement)  CRJ 700  CRJ 900 33 16  Individual aircraft have scheduled removal dates under the agreement during 2018 SkyWest Airlines Delta Connection Prorate Agreement (revenue-sharing arrangement)  CRJ 200 24  Terminable with 30-day notice United Express Agreements Agreement Aircraft type Number of Aircraft Term / Termination SkyWest Airlines United Express Agreements (fixed-fee arrangement)  CRJ 200  CRJ 700  E175 57 20 65  Individual aircraft have scheduled removal dates under the agreement between 2018 and 2029  The average remaining term of the aircraft under contract is 5.1 years ExpressJet United ERJ Agreement (fixed-fee arrangement)  ERJ145  ERJ135 109 3  Agreement expires in 2022  The average remaining term of the aircraft under contract is 4.8 years SkyWest Airlines United Express Prorate Agreement (revenue-sharing arrangement)  CRJ 200 24  Terminable with 120-day notice American Agreements Agreement Aircraft type Number of Aircraft Term / Termination Dates SkyWest Airlines American Agreement (fixed-fee arrangement)  CRJ 200  CRJ 700 10 37  CRJ200 aircraft are scheduled to expire in 2018 and the CRJ700 aircraft are scheduled to expire in 2019 SkyWest Airlines American Prorate Agreement (revenue-sharing arrangement)  CRJ 200 6  Terminable with 120-day notice ExpressJet American Agreement (fixed-fee arrangement)  CRJ 700 12  CRJ700 aircraft are scheduled to expire in 2019 Alaska Capacity Purchase Agreement Agreement Aircraft type Number of Aircraft Term / Termination SkyWest Airlines Alaska Agreement (fixed-fee arrangement)  CRJ 200  E175 4 23  CRJ200 aircraft are scheduled to expire in 2018  E175 aircraft have scheduled removal dates under the agreement between 2027 and 2029 In addition to the contractual arrangements described above, SkyWest Airlines has entered into agreements with Alaska and Delta to place additional E175/E175 SC aircraft into service for those major airline partners. As of December 31, 2017, the Company anticipated placing an additional 12 E175 aircraft with Alaska and 30 E175 SC aircraft with Delta. The delivery dates for the new E175/E175 SC aircraft are currently scheduled to take place by the end of 2018 or early 2019. Final delivery dates may adjust based on various factors. ExpressJet initiated the wind down of its flying agreement with Delta during 2017 and expected to be complete by the end of 2018. As of December 31, 2017, ExpressJet operated 49 CRJ700s/900s under its Delta flying agreement. Of the 49 aircraft, ExpressJet anticipates returning 19 leased aircraft to Delta and removing 30 CRJ700 aircraft from service with Delta during 2018. ExpressJet is pursuing placement of the 30 CRJ700 aircraft with other partners, of which eight aircraft are scheduled to be placed under an agreement with American following the removal from service with Delta.
Deferred Aircraft Credits	Deferred Aircraft Credits The Company accounts for incentives provided by aircraft manufacturers as deferred credits. The deferred credits related to leased aircraft are amortized on a straight‑line basis as a reduction to rent expense over the lease term. Credits related to owned aircraft reduce the purchase price of the aircraft, which has the effect of amortizing the credits on a straight‑line basis as a reduction in depreciation expense over the life of the related aircraft. The incentives are credits that may be used to purchase spare parts and pay for training and other expenses
Income Taxes	Income Taxes The Company recognizes a net liability or asset for the deferred tax consequences of all temporary differences between the tax basis of assets and liabilities and their reported amounts in the consolidated financial statements that are expected to result in taxable or deductible amounts in future years when the reported amounts of the assets and liabilities are recovered or settled.
Net Income (Loss) Per Common Share	Net Income (Loss) Per Common Share Basic net income (loss) per common share (“Basic EPS”) excludes dilution and is computed by dividing net income (loss) by the weighted average number of common shares outstanding during the period. Diluted net income (loss) per common share (“Diluted EPS”) reflects the potential dilution that could occur if stock options or other contracts to issue common stock were exercised or converted into common stock. The computation of Diluted EPS does not assume exercise or conversion of securities that would have an anti‑dilutive effect on net income (loss) per common share. During the year ended December 31, 2017, 284,000 performance shares (at target performance) were excluded in the computation of Diluted EPS since the Company had not achieved the minimum target thresholds as of December 31, 2017. During the year ended December 31, 2016, 2,077,000 shares reserved for the issuance upon the exercise of outstanding options, performance shares and restricted stock units were excluded from the computation of Diluted EPS due to the net loss in 2016 and 505,000 shares reserved for outstanding options were excluded from the Diluted EPS calculation for the year ended December 31, 2015 as the respective exercise price exceeded the weighted average fair market value of the Company’s stock for 2015. The calculation of the weighted average number of common shares outstanding for Basic EPS and Diluted EPS are as follows for the years ended December 31, 2017, 2016 and 2015 (in thousands): Year Ended December 31, 2017 2016 2015 Numerator: Net Income (Loss) $ 428,907 $ (161,586) $ 117,817 Denominator: Denominator for basic earnings per-share weighted average shares 51,804 51,505 51,077 Dilution due to stock options and restricted stock units 1,296 — 748 Denominator for diluted earnings per-share weighted average shares 53,100 51,505 51,825 Basic earnings (loss) per-share $ 8.28 $ (3.14) $ 2.31 Diluted earnings (loss) per-share $ 8.08 $ (3.14) $ 2.27
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) includes charges and credits to stockholders’ equity that are not the result of transactions with the Company’s shareholders, including changes in unrealized appreciation on marketable securities.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts reported in the consolidated balance sheets for receivables and accounts payable approximate fair values because of the immediate or short‑term maturity of these financial instruments. Marketable securities are reported at fair value based on market quoted prices in the consolidated balance sheets. If quoted prices in active markets are no longer available, the Company has estimated the fair values of these securities utilizing a discounted cash flow analysis as of December 31, 2017. These analyses consider, among other items, the collateralization underlying the security investments, the creditworthiness of the counterparty, the timing of expected future cash flows, and the expectation of the next time the security is expected to have a successful auction. The fair value of the Company’s long‑term debt is estimated based on current rates offered to the Company for similar debt and was approximately $2,698.4 million as of December 31, 2017, as compared to the carrying amount of $2,712.4 million as of December 31, 2017. The Company’s fair value of long‑term debt as of December 31, 2016 was $2,566.5 million as compared to the carrying amount of $2,570.9 million as of December 31, 2016.
Segment Reporting	Segment Reporting Generally accepted accounting principles require disclosures related to components of a company for which separate financial information is available to, and regularly evaluated by, the Company’s chief operating decision maker when deciding how to allocate resources and in assessing performance. The Company’s three operating segments consist of the operations conducted by SkyWest Airlines, ExpressJet and SkyWest Leasing. Information pertaining to the Company’s reportable segments is presented in Note 2, Segment Reporting .
Recent Accounting Pronouncements	Recent Accounting Pronouncements Standards Effective in Future Years and Not Yet Adopted In May 2014, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update No. 2014‑09, “Revenue from Contracts with Customers” (“ASU No. 2014‑09”). Under ASU No. 2014‑09, revenue is recognized at the time a good or service is transferred to a customer for the amount of consideration received for that specific good or service. In 2016, the FASB issued several amendments to the standard, including principal versus agent considerations when another party is involved in providing goods or services to a customer and the application of identifying performance obligations. The Company’s adoption of the standard as of January 1, 2018, will be first presented in the first quarter of 2018, utilizing the full retrospective method of adoption allowed by the standard, in order to provide for comparative results in all periods presented. Under the new standard, the Company concluded that individual flights are distinct services and these flight services promised in a CPA agreement represent a series of services that should be accounted for as a single performance obligation, recognized over time as the flights are completed. The adoption of ASU No. 2014‑09 did not have a material impact on recorded amounts when applied to the opening balance sheet as of January 1, 2018 and is not expected to impact the amount or timing of the future amounts of net income, however the principal versus agent considerations under ASU No. 2014-09 will result in the Company recording directly reimbursed fuel expense under its fixed-fee contracts as a reduction to the applicable operating expense (net) rather than revenue (gross). The Company’s analysis of information necessary to recast prior period results is still preliminary and additional impacts could still result when the standard is first applied to revenue transactions during the first quarter of 2018. In February 2016, the FASB issued Accounting Standards Update 2016‑02, “Leases (Topic 842)” (“ASU No. 2016-02”). ASU No. 2016‑02 amends the existing accounting standards for lease accounting, including requiring lessees to recognize most leases on their balance sheets and making targeted changes to lessor accounting. ASU No. 2016‑02 will be effective beginning in the first quarter of 2019. Early adoption of ASU No. 2016‑02 is permitted. ASU No. 2016‑02 requires a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application, with an option to use certain transition relief. The Company’s management is currently evaluating the impact the adoption of ASU 2016‑02 is anticipated to have on the Company’s consolidated financial statements. In 2016, the FASB issued Accounting Standards Update 2016‑15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” and Accounting Standard Update 2016‑18, “Statement of Cash Flows (Topic 230): Restricted Cash” related to the classification of certain cash receipts and cash payments and the presentation of restricted cash within an entity’s statement of cash flows, respectively. These standards are effective for interim and annual reporting periods beginning after December 15, 2017, but early adoption is permitted. The Company anticipates adopting this standard in the first quarter of 2018 that will modify the presentation of changes in restricted cash in the Company’s Consolidated Statement of Cash Flows. Recently Adopted Standards Pursuant to the guidelines of the recently issued Accounting Standards Update 2015-17, “Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes” (“ASU 2015‑17”), all net deferred tax assets and liabilities are to be classified as non-current. As permitted under ASU 2015‑17, the Company adopted this guidance for the quarter ended March 31, 2017. The Company adopted ASU 2015‑17 retrospectively. Upon adoption, approximately $129.3 million of formerly recorded current deferred tax assets as of December 31, 2016 were reclassified to non-current and netted against non-current deferred income taxes payable as of December 31, 2016 in the accompanying financial statements. In March 2016, the FASB issued Accounting Standards Update No. 2016‑09, “Compensation—Stock Compensation (Topic 718)” (“ASU No. 2016‑09”). ASU No. 2016‑09 makes several amendments to Topic 718, which simplified the accounting for share-based payment transactions, including the income tax consequences, the calculation of diluted earnings per share, the treatment of forfeitures and the classification on the statement of cash flows. Amendments related to the timing of when excess tax benefits are recognized, minimum statutory withholding requirements and forfeitures should be applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity as of the beginning of the period in which the guidance is adopted. Amendments requiring the recognition of excess tax benefits and tax deficiencies in the income statement should be applied prospectively. Prior to the adoption of ASU No. 2016‑09, accounting principles generally accepted in the United States of America (“GAAP”) required tax effects of deductions for share-based payments in excess of compensation cost and tax deficiencies to be recorded in equity. Under ASU No. 2016‑09, the tax effects of awards are treated as discrete income tax expense items in the reporting period in which they occur. The Company adopted ASU No. 2016‑09 as of January 1, 2017. The adoption of this standard resulted in the recognition in of $0.9 million of previously unrecognized excess tax benefits in net deferred tax liabilities and an increase to retained earnings on the consolidated balance sheet as of the beginning of the current year, and the recognition of $5.4 million of excess tax benefits in the income tax provision for the year ended December 31, 2017. The adoption of ASU No. 2016‑09 did not have a material impact on the statement of cash flows presentation.

Nature of Operations and Summ23

Nature of Operations and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Schedule of the Company's position in marketable securities	The Company’s position in marketable securities as of December 31, 2017 and 2016 was as follows (in thousands): Gross unrealized Gross unrealized At December 31, 2017 Amortized Cost holding gains holding losses Fair market value Total cash and cash equivalents $ 181,792 $ — $ — $ 181,792 Marketable securities: Bond and bond funds $ 344,479 $ — $ (228) $ 344,251 Commercial Paper 159,252 — — 159,252 Total marketable securities $ 503,731 $ — $ (228) $ 503,503 Total assets measured at fair value $ 685,523 $ — $ (228) $ 685,295 Gross unrealized Gross unrealized At December 31, 2016 Amortized Cost holding gains holding losses Fair market value Total cash and cash equivalents $ 146,766 $ — $ — $ 146,766 Marketable securities: Bond and bond funds $ 410,001 $ — $ (116) $ 409,885 Commercial Paper 13 — — 13 Total marketable securities $ 410,014 $ — $ (116) $ 409,898 Total assets measured at fair value $ 556,780 $ — $ (116) $ 556,664
Schedule of property and equipment	Assets Current Depreciable Life Prior Policy Depreciable Life Current Residual Value Prior Policy Residual Value New Aircraft 20 - 22 years 18 years 17.5 - 20 % % Used Aircraft, rotable spares, and spare engines up to 18 years up to 18 years 0 - 20 % 0 - 30 % Ground equipment up to 10 years No Change 0 % No Change Office equipment up to 7 years No Change % No Change Leasehold improvements Shorter of 15 years or lease term No Change % No Change Buildings 20 - 39.5 years No Change % No Change
Schedule of net income (loss) per common share	Year Ended December 31, 2017 2016 2015 Numerator: Net Income (Loss) $ 428,907 $ (161,586) $ 117,817 Denominator: Denominator for basic earnings per-share weighted average shares 51,804 51,505 51,077 Dilution due to stock options and restricted stock units 1,296 — 748 Denominator for diluted earnings per-share weighted average shares 53,100 51,505 51,825 Basic earnings (loss) per-share $ 8.28 $ (3.14) $ 2.31 Diluted earnings (loss) per-share $ 8.08 $ (3.14) $ 2.27
Delta Connection Agreements
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Schedule of details of aircraft and agreements with other airlines	Agreement Aircraft type Number of Aircraft Term / Termination SkyWest Airlines Delta Connection Agreement (fixed-fee arrangement)  CRJ 200  CRJ 700  CRJ 900  E175 70 27 36 19  Individual aircraft have scheduled removal dates under the agreement between 2018 and 2027  The average remaining term of the aircraft under contract is 2.9 years ExpressJet Delta Connection Agreement (fixed-fee arrangement)  CRJ 700  CRJ 900 33 16  Individual aircraft have scheduled removal dates under the agreement during 2018 SkyWest Airlines Delta Connection Prorate Agreement (revenue-sharing arrangement)  CRJ 200 24  Terminable with 30-day notice
United Express Agreements
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Schedule of details of aircraft and agreements with other airlines	Agreement Aircraft type Number of Aircraft Term / Termination SkyWest Airlines United Express Agreements (fixed-fee arrangement)  CRJ 200  CRJ 700  E175 57 20 65  Individual aircraft have scheduled removal dates under the agreement between 2018 and 2029  The average remaining term of the aircraft under contract is 5.1 years ExpressJet United ERJ Agreement (fixed-fee arrangement)  ERJ145  ERJ135 109 3  Agreement expires in 2022  The average remaining term of the aircraft under contract is 4.8 years SkyWest Airlines United Express Prorate Agreement (revenue-sharing arrangement)  CRJ 200 24  Terminable with 120-day notice
American Agreements
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Schedule of details of aircraft and agreements with other airlines	Agreement Aircraft type Number of Aircraft Term / Termination Dates SkyWest Airlines American Agreement (fixed-fee arrangement)  CRJ 200  CRJ 700 10 37  CRJ200 aircraft are scheduled to expire in 2018 and the CRJ700 aircraft are scheduled to expire in 2019 SkyWest Airlines American Prorate Agreement (revenue-sharing arrangement)  CRJ 200 6  Terminable with 120-day notice ExpressJet American Agreement (fixed-fee arrangement)  CRJ 700 12  CRJ700 aircraft are scheduled to expire in 2019
Alaska Capacity Purchase Agreement
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Schedule of details of aircraft and agreements with other airlines	Agreement Aircraft type Number of Aircraft Term / Termination SkyWest Airlines Alaska Agreement (fixed-fee arrangement)  CRJ 200  E175 4 23  CRJ200 aircraft are scheduled to expire in 2018  E175 aircraft have scheduled removal dates under the agreement between 2027 and 2029

Segment Reporting (Tables)

Segment Reporting (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting
Schedule of Company's segment data	The following represents the Company’s segment data for the years ended December 31, 2017, 2016 and 2015 (in thousands). Year Ended December 31, 2017 SkyWest Airlines ExpressJet SkyWest Leasing Consolidated Operating revenues $ 2,173,384 $ 790,942 $ 239,942 $ 3,204,268 Operating expense 1,888,556 819,343 108,170 2,816,069 Depreciation and amortization expense 134,563 51,982 106,223 292,768 Interest expense 21,544 4,127 79,254 104,925 Segment profit (loss) (1) 263,284 (32,528) 52,518 283,274 Identifiable intangible assets, other than goodwill — 4,896 — 4,896 Total assets 2,228,930 599,122 2,630,227 5,458,279 Capital expenditures (including non-cash) 124,955 14,278 550,165 689,398 Year Ended December 31, 2016 SkyWest Airlines ExpressJet SkyWest Leasing Consolidated Operating revenues $ 1,935,378 $ 1,044,828 $ 141,000 $ 3,121,206 Operating expense 1,886,173 1,339,569 68,148 3,293,890 Depreciation and amortization expense 139,159 83,935 61,875 284,969 Special items 184,295 281,354 — 465,649 Interest expense 26,211 6,773 45,193 78,177 Segment profit (loss) (1) 22,994 (301,514) 27,659 (250,861) Identifiable intangible assets, other than goodwill — 8,249 — 8,249 Total assets 2,250,276 582,890 2,174,800 5,007,966 Capital expenditures (including non-cash) 57,761 15,396 1,085,844 1,159,001 Year Ended December 31, 2015 SkyWest Airlines ExpressJet SkyWest Leasing Consolidated Operating revenues $ $ $ $ 3,095,563 Operating expense 38,778 2,861,048 Depreciation and amortization expense 264,507 Interest expense 75,850 Segment profit (loss) (1) 182,022 (34,238) 10,881 158,665 Identifiable intangible assets, other than goodwill — — 10,499 Total assets 4,781,984 Capital expenditures (including non-cash) 715,089 Segment profit is operating income less interest expense

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Long-Term Debt
Schedule of long-term debt	Long‑term debt consisted of the following as of December 31, 2017 and 2016 (in thousands): December 31, December 31, 2017 2016 Notes payable to banks, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.91% to 3.43% through 2020, secured by aircraft $ 34,905 $ Notes payable to a financing company, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.85% to 3.25% through 2021, secured by aircraft 97,612 Notes payable to banks, due in semi-annual installments plus interest at 6.06% to 6.51% through 2021, secured by aircraft 63,090 Notes payable to a financing company, due in semi-annual installments plus interest at 5.78% to 6.23% through 2017, secured by aircraft — Notes payable to banks, due in monthly installments plus interest of 2.68% to 6.86% through 2025, secured by aircraft 372,157 Notes payable to banks, due in monthly installments, plus interest at 4.16% to 6.05% through 2029, secured by aircraft 49,001 Notes payable to banks, due in monthly installments, plus interest at 3.44% through 2019, secured by aircraft — Notes payable to banks, due in quarterly installments, plus interest at 3.39% to 4.73% through 2029, secured by aircraft 2,085,822 Notes payable to banks, due in monthly installments, plus interest based on LIBOR at 3.54% through 2017, secured by aircraft — Notes payable to banks due in monthly installments, interest at 3.30% through 2019, secured by spare engines 9,763 Long-term debt $ 2,712,350 $ Current portion of long-term debt (313,243) (308,945) Less long-term portion of unamortized debt issue cost, net (21,761) (21,908) Long-term debt, net of current maturities and debt issue costs $ 2,377,346 $ 2,240,051 Current portion of long-term debt 313,243 308,945 Less current portion of unamortized debt issue cost, net (3,565) (3,485) Current portion of long-term debt, net of debt issue costs $ 309,678 $ 305,460
Schedule of maturities of long-term debt	The aggregate amounts of principal maturities of long‑term debt as of December 31, 2017 were as follows (in thousands): 2018 $ 313,243 2019 2020 2021 2022 Thereafter $ 2,712,350

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Taxes
Schedule of components of provision (benefit) for income taxes	The provision (benefit) for income taxes includes the following components (in thousands): Year ended December 31, 2017 2016 2015 Current tax provision (benefit): Federal $ 5,853 $ (3,801) $ 3,801 State 180 111 1,035 6,033 (3,690) 4,836 Deferred tax provision (benefit): Federal (166,890) (77,430) 66,430 State 20,133 (6,106) 5,239 (146,757) (83,536) 71,669 Provision (benefit) for income taxes $ (140,724) $ (87,226) $ 76,505
Schedule of income tax rate reconciliation	The following is a reconciliation between a federal income tax rate of 35% of income (loss) before income taxes and the effective tax rate which is derived by dividing the provision (benefit) for income taxes by income (loss) before for income taxes (in thousands): Year ended December 31, 2017 2016 2015 Computed provision (benefit) for income taxes at the statutory rate $ 100,864 $ (87,084) $ 68,013 Increase (decrease) in income taxes resulting from: State income tax provision (benefit), net of federal income tax benefit 7,778 (5,768) 5,416 Non-deductible expenses 3,230 3,552 3,641 Valuation allowance changes affecting the provision for income taxes 505 751 (899) Excess tax benefits from share-based compensation (5,377) — — Revaluation of net deferred taxes for the Tax Act (246,845) — — Other, net (879) 1,323 334 Provision (benefit) for income taxes $ (140,724) $ (87,226) $ 76,505
Schedule of components of the net deferred tax assets and liabilities	The significant components of the Company’s net deferred tax assets and liabilities as of December 31, 2017 and 2016 are as follows (in thousands): As of December 31, 2017 2016 Deferred tax assets: Intangible asset $ (206) $ 4,983 Accrued benefits 31,651 48,482 Net operating loss carryforward 122,648 286,389 AMT credit carryforward 23,443 17,589 Deferred aircraft credits 53,870 60,415 Accrued reserves and other 26,853 47,906 Total deferred tax assets 258,259 465,764 Valuation allowance (10,642) (8,877) Deferred tax liabilities: Accelerated depreciation (666,637) (1,022,291) Total deferred tax liabilities (666,637) (1,022,291) Net deferred tax liability $ (419,020) $ (565,404)

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies
Schedule of Future Minimum Rental Payments for Operating Leases	The following table summarizes future minimum rental payments required under operating leases that have non‑cancelable lease terms as of December 31, 2017 (in thousands): 2018 $ 142,157 2019 104,297 2020 121,119 2021 112,657 2022 75,981 Thereafter 160,621 $ 716,832
Schedule of Employees Under Collective Bargaining Agreements	Approximate Number of Active Employees Status of Employee Group Represented Representatives Agreement Atlantic Southeast Pilots Air Line Pilots Association International Amendable February 2018 Atlantic Southeast Flight Attendants International Association of Machinists and Aerospace Workers Currently Amendable Atlantic Southeast Flight Controllers Transport Workers Union of America Currently Amendable Atlantic Southeast Mechanics International Brotherhood of Teamsters Currently Amendable Atlantic Southeast Stock Clerks International Brotherhood of Teamsters Currently Amendable ExpressJet Delaware Pilots Air Line Pilots Association International Amendable February 2018 ExpressJet Delaware Flight Attendants International Association of Machinists and Aerospace Workers Currently Amendable ExpressJet Delaware Mechanics International Brotherhood of Teamsters Amendable January 2019 ExpressJet Delaware Dispatchers Transport Workers Union of America Currently Amendable ExpressJet Delaware Stock Clerks International Brotherhood of Teamsters Currently Amendable

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Measurements
Schedule of assets measured at fair value on a recurring basis	As of December 31, 2017, the Company held certain assets that are required to be measured at fair value on a recurring basis. Assets measured at fair value on a recurring basis are summarized below (in thousands): Fair Value Measurements as of December 31, 2017 Total Level 1 Level 2 Level 3 Marketable Securities Bonds and bond funds $ $ — $ $ — Commercial paper — — $ $ — $ $ — Cash, Cash Equivalents and Restricted Cash — — Total Assets Measured at Fair Value $ $ $ $ — Fair Value Measurements as of December 31, 2016 Total Level 1 Level 2 Level 3 Marketable Securities Bonds and bond funds $ $ — $ $ — Commercial paper — 13 — $ $ — $ $ — Cash, Cash Equivalents and Restricted Cash — — Total Assets Measured at Fair Value $ $ $ $ —

Special Items (Tables)

Special Items (Tables)	12 Months Ended
	Dec. 31, 2017
Special Items
Summary of the components of special items	The following table summarizes the components of the Company's special items, for the year ended December 31, 2017, 2016 and 2015 (in thousands): Year ended December 31, 2017 2016 2015 Special items: CRJ200 aircraft related items 1 $ — $ 424,466 $ — ERJ145 aircraft related items 2 — 41,183 — Total special items $ — $ 465,649 $ — (1) Consists primarily of inventory valuation charges and impairment charges to write-down CRJ200 aircraft including related long-lived assets to their estimated fair value. The estimated fair value of the long-lived assets, including the aircraft and fixed asset spare parts inventory, was based on third-party appraisals on the assets. These values were estimated based on listed market values or recent third-party market transactions for similar assets. Additionally, the Company estimated the fair value of certain long-lived prepaid lease assets using the net present value of estimated current CRJ200 lease rates. All fair values are considered to be Level 3 within the fair value hierarchy. Of the special items $184.3 million related to SkyWest Airlines and $240.2 million related to ExpressJet. These charges are net of $90 million in cash proceeds and other considerations from the Bombardier termination agreement. These special items are reflected in the SkyWest Airlines and ExpressJet operating expenses under Note 2 Segment Reporting. (2) The ERJ145 aircraft related items recorded in the 2016 special charge consist primarily of inventory valuation charges and impairment charges to write-down certain ERJ145 long-lived assets, which primarily consisted of spare engines and ERJ145 spare aircraft parts, to their estimated fair value of $41.2 million. The estimated fair value of the long-lived assets was based on third-party appraisals and valuations for similar assets which is considered an unobservable input (Level 3) under the fair value hierarchy. These special items are reflected in the ExpressJet operating expenses under Note 2 Segment Reporting .

Capital Transactions (Tables)

Capital Transactions (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule of assumptions used and weighted average fair value for stock option grants	2016 2015 Expected annual dividend rate 1.08 % 1.18 % Risk-free interest rate 1.15 % 1.62 % Average expected life (years) 5.7 5.7 Expected volatility of common stock 0.412 0.401 Forfeiture rate % % Weighted average fair value of option grants $ 5.27 $ 4.75
Schedule of restricted stock activity	During the year ended December 31, 2016, the Company granted 380,358 shares of restricted stock units to certain Company’s employees under the 2010 Incentive Plan. The restricted stock units granted during the year ended December 31, 2016 have a three‑year vesting period, during which the recipient must remain employed with the Company or its subsidiaries. The weighted average fair value of the restricted stock units the date of grants made during the year ended December 31, 2016 was $14.81 per share. The following table summarizes the activity of restricted stock units granted to certain Company employees as of December 31, 2016, 2015 and 2014: Weighted-Average Grant-Date Fair Number of Shares Value Non-vested shares outstanding at December 31, 2014 723,176 $ 12.70 Granted 408,163 13.57 Vested (215,856) 13.06 Cancelled (106,184) 13.52 Non-vested shares outstanding at December 31, 2015 809,299 $ 13.13 Granted 384,148 14.81 Vested (215,146) 13.29 Cancelled (51,370) 13.72 Non-vested shares outstanding at December 31, 2016 926,931 $ 13.65 Granted 160,137 35.81 Vested (230,903) 12.01 Cancelled (40,575) 15.78 Non-vested shares outstanding at December 31, 2017 815,590 $ 18.35
Schedule of stock option activity	2017 2016 2015 Weighted Weighted Average Aggregate Weighted Weighted Average Remaining Intrinsic Average Average Number of Exercise Contractual Value Number of Exercise Number of Exercise Options Price Term ($000) Options Price Options Price Outstanding at beginning of year 819,981 $ 13.58 4.4 years $ 18,756.9 1,064,429 $ 13.64 2,888,074 $ 16.46 Granted — — 206,021 14.90 267,433 Exercised (356,209) 13.36 (351,296) 14.17 (544,917) Cancelled (5,669) 14.33 (99,173) 14.90 (1,546,161) Outstanding at end of year 458,103 13.73 4.0 years $ 18,034.1 819,981 13.58 1,064,429 Exercisable at December 31, 2017 254,192 13.17 3.4 years $ 10,150.8 Exercisable at December 31, 2016 263,851 13.76 2.8 years $ 5,985.5
Schedule of non-vested stock options	The following table summarizes the status of the Company’s non‑vested stock options as of December 31, 2017: Weighted-Average Number of Grant-Date Shares Fair Value Non-vested shares at beginning of year 556,130 $ 4.86 Granted — — Vested (346,550) 4.67 Cancelled (5,669) 5.14 Non-vested shares at end of year $ 5.17
Schedule of stock options outstanding	The following table summarizes information about the Company’s stock options outstanding at December 31, 2017: Options Outstanding Options Exercisable Weighted Average Number Remaining Weighted Average Number Weighted Average Range of Exercise Prices Outstanding Contractual Life Exercise Price Exercisable Exercise Price $8.00 to $12.99 3.1 years $ 12.06 $ $13.00 to $14.99 4.2 years $15.00 to $19.00 4.8 years $8.00 to $19.00 4.0 years $ $
Performance share units
Schedule of non-vested stock options	The following table summarizes the activity of performance share units granted at target as of December 31, 2017. Weighted-Average Grant-Date Fair Number of Shares Value Non-vested shares outstanding at December 31, 2014 — $ — Granted 13.61 Vested — — Cancelled (19,754) 13.51 Non-vested shares outstanding at December 31, 2015 202,829 $ 13.62 Granted 14.89 Vested — — Cancelled (22,413) 14.16 Non-vested shares outstanding at December 31, 2016 363,993 $ 14.23 Granted 35.81 Vested — — Cancelled (14,732) 15.00 Non-vested shares outstanding at December 31, 2017 $ 19.70

Retirement Plans and Employee31

Retirement Plans and Employee Stock Purchase Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Plans and Employee Stock Purchase Plans
Schedule of purchases made under the 2009 Employee Stock Purchase Plans	Year ended December 31, 2017 2016 2015 Number of shares purchased 88,362 151,531 254,098 Average price of shares purchased $ 33.96 $ 20.87 $ 13.50

Quarterly Financial Data (Una32

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data (Unaudited)
Schedule of Quarterly Financial Data (Unaudited)	Year ended December 31, 2017 First Second Third Fourth Quarter Quarter Quarter Quarter Year Operating revenues $ 765,415 $ 809,759 $ 831,936 $ 797,158 $ Operating income 76,295 106,596 112,369 92,939 388,199 Net income(1) 34,786 50,477 53,716 289,928 428,907 Net income per common share: Basic 5.60 8.28 Diluted 5.46 8.08 Weighted average common shares: Basic: 51,820 51,751 51,833 51,811 51,804 Diluted: 53,202 52,977 53,080 53,140 53,100 Year ended December 31, 2016 First Second Third Fourth Quarter Quarter Quarter Quarter Year Operating revenues $ 762,075 $ 801,338 $ 799,776 $ $ Operating income (loss) 61,809 84,137 85,834 (172,684) Net income (loss)(2) 27,092 40,244 41,322 (161,586) Net income (loss) per common share: Basic Diluted Weighted average common shares: Basic: 51,218 51,418 51,627 Diluted: 52,014 52,194 52,471 (1) Net income for 2017 included a $246.8 million benefit related to the revaluation of the Company’s deferred tax liability and other tax liabilities in accordance with the Tax Act. Operating loss for the fourth quarter of 2016 included a special charge of $465.6 million related to an impairment on the Company’s 50-seat aircraft

Nature of Operations and Summ33

Nature of Operations and Summary of Significant Accounting Policies - Aircraft Fleet (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2016item	Dec. 31, 2017itemaircraft
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of daily departures to different destinations | item		2,980
Number of aircraft held by entity		623
Number of seats on aircraft | item	50
CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		208
CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		136
CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		52
ERJ 135
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		3
ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		117
E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		107
Number of seats on aircraft | item		76
E175 SC
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of seats on aircraft | item		70
Number of aircraft ordered		30
EMB 120
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft removed from service		11
Number of seats on aircraft | item		30
United
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		278
Percentage of aggregate capacity operated		46.70%
United | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		81
United | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		20
United | ERJ 135
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		3
United | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		109
United | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		65
Delta
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		225
Percentage of aggregate capacity operated		37.80%
Delta | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		94
Delta | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		60
Delta | CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		52
Delta | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		19
American
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		65
Percentage of aggregate capacity operated		10.90%
American | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		16
American | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		49
Alaska
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		27
Percentage of aggregate capacity operated		4.60%
Alaska | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		4
Alaska | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		23
Aircraft in scheduled service
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		595
Aircraft in scheduled service | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		195
Aircraft in scheduled service | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		129
Aircraft in scheduled service | CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		52
Aircraft in scheduled service | ERJ 135
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		3
Aircraft in scheduled service | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		109
Aircraft in scheduled service | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		107
Subleased to an un-affiliated entity
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		4
Subleased to an un-affiliated entity | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		4
Other
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		24
Other | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		9
Other | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		7
Other | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		8

Nature of Operations and Summ34

Nature of Operations and Summary of Significant Accounting Policies - Cash and Cash Equivalents (Details) $ in Thousands	Dec. 31, 2016USD ($)
Nature of Operations and Summary of Significant Accounting Policies
Restricted cash	$ 8,243

Nature of Operations and Summ35

Nature of Operations and Summary of Significant Accounting Policies - Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Marketable Securities
Total cash and cash equivalents	$ 181,792	$ 146,766	$ 203,035	$ 132,275
Amortized Cost	503,731	410,014
Gross unrealized holding losses	(228)	(116)
Marketable securities	503,503	409,898
Total Assets Measured at Fair Value - Amortized cost	685,523	556,780
Total cash and cash equivalents and available for sale securities, fair market value	$ 685,295	556,664
Marketable Securities
Maximum period for redemption	1 year
Bonds and bond funds
Marketable Securities
Amortized Cost	$ 344,479	410,001
Gross unrealized holding losses	(228)	(116)
Marketable securities	344,251	409,885
Commercial paper
Marketable Securities
Amortized Cost	159,252	13
Marketable securities	$ 159,252	$ 13

Nature of Operations and Summ36

Nature of Operations and Summary of Significant Accounting Policies - Inventories (Details) $ in Millions	3 Months Ended
	Dec. 31, 2016USD ($)item	Dec. 31, 2017USD ($)
Inventories
Inventory allowance | $	$ 40.5	$ 17.1
Number of seats on aircraft | item	50

Nature of Operations and Summ37

Nature of Operations and Summary of Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment
Increased depreciation expense	$ 1.4
New aircraft
Property and Equipment
Depreciable Life		18 years
Residual Value (as a percent)		30.00%
New aircraft | Minimum
Property and Equipment
Depreciable Life	20 years
Residual Value (as a percent)	17.50%
New aircraft | Maximum
Property and Equipment
Depreciable Life	22 years
Residual Value (as a percent)	20.00%
Used Aircraft, rotable spares, and spare engines | Minimum
Property and Equipment
Residual Value (as a percent)	0.00%	0.00%
Used Aircraft, rotable spares, and spare engines | Maximum
Property and Equipment
Depreciable Life	18 years	18 years
Residual Value (as a percent)	20.00%	30.00%
Ground equipment
Property and Equipment
Residual Value (as a percent)	0.00%
Ground equipment | Maximum
Property and Equipment
Depreciable Life	10 years
Office equipment
Property and Equipment
Residual Value (as a percent)	0.00%
Office equipment | Maximum
Property and Equipment
Depreciable Life	7 years
Leasehold improvements
Property and Equipment
Residual Value (as a percent)	0.00%
Leasehold improvements | Maximum
Property and Equipment
Depreciable Life	15 years
Buildings
Property and Equipment
Residual Value (as a percent)	0.00%
Buildings | Minimum
Property and Equipment
Depreciable Life	20 years
Buildings | Maximum
Property and Equipment
Depreciable Life	39 years 6 months

Nature of Operations and Summ38

Nature of Operations and Summary of Significant Accounting Policies - Long-Lived Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 07, 2005
Impairment of Long Lived and Intangible Assets
Property and equipment and related assets	$ 5,650,478	$ 5,140,005
Intangible assets	4,896	8,249	$ 10,499
Impairment of long-lived assets	0
Proceeds from settlement of residual value guarantee aircraft agreements		90,000
Atlantic Southeast Airlines Inc.
Impairment of Long Lived and Intangible Assets
Intangible assets related to acquisition of Atlantic Southeast				$ 33,700
Accumulated amortization expense	$ 28,900	$ 25,500

Nature of Operations and Summ39

Nature of Operations and Summary of Significant Accounting Policies - Capitalized Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Capitalized Interest
Capitalized interest costs	$ 1.4	$ 1.5	$ 2.2

Nature of Operations and Summ40

Nature of Operations and Summary of Significant Accounting Policies - Passenger and Ground Handling Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ExpressJet United Express ERJ Agreement and ExpressJet American ERJ145 Agreement
Other Revenue Items
Deemed rental income under code-share agreement	$ 572.7	$ 516	$ 504.9

Nature of Operations and Summ41

Nature of Operations and Summary of Significant Accounting Policies - Agreements (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2016item	Dec. 31, 2018aircraft	Dec. 31, 2017agreementaircraftitem
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			623
Number of seats on aircraft | item	50
CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			208
CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			136
CRJ 700 | Forecast
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft removed from service		8
CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			52
CRJ 700s/900s
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft operated | agreement			49
CRJ 700s/900s | Forecast
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of leased aircraft returned		19
Number of aircraft removed from service		30
E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			107
Number of seats on aircraft | item			76
E 175 | Forecast
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of additional aircraft placed into service		12
E175 SC
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of seats on aircraft | item			70
E175 SC | Forecast
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of additional aircraft placed into service		30
ERJ 135
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			3
ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			117
EMB 120
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft removed from service			11
Number of seats on aircraft | item			30
Delta Connection Agreements | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			70
Delta Connection Agreements | CRJ 700 | ExpressJet
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			33
Delta Connection Agreements | CRJ 900 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			36
Delta Connection Agreements | CRJ 900 | ExpressJet
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			16
Delta Connection Agreements | E 175 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			19
Term of agreement			2 years 10 months 24 days
Delta Connection Prorate Agreements | CRJ 200 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			24
Term of agreement			30 days
Delta Connection Prorate Agreements | CRJ 700 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			27
United Express Agreements | CRJ 200 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			57
United Express Agreements | CRJ 700 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			20
United Express Agreements | E 175 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			65
Term of agreement			5 years 1 month 6 days
United ERJ Agreements | ERJ 135 | ExpressJet
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			3
Term of agreement			4 years 9 months 18 days
United ERJ Agreements | ERJ 145 | ExpressJet
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			109
United Express Prorate Agreement | CRJ 200 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			24
Term of agreement			120 days
American Agreements | CRJ 200 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			10
American Agreements | CRJ 700 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			37
American Capacity Purchase Agreement | CRJ 700 | ExpressJet
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			12
American Prorate Agreement | CRJ 200 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			6
Term of agreement			120 days
Alaska Capacity Purchase Agreement | CRJ 200 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			4
Alaska Capacity Purchase Agreement | E 175 | Sky West Airlines Inc
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft			23
American
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			65
American | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			16
American | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			49
Aircraft in scheduled service
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			595
Aircraft in scheduled service | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			195
Aircraft in scheduled service | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			129
Aircraft in scheduled service | CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			52
Aircraft in scheduled service | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			107
Aircraft in scheduled service | ERJ 135
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			3
Aircraft in scheduled service | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity			109

Nature of Operations and Summ42

Nature of Operations and Summary of Significant Accounting Policies - Net Income (Loss) Per Share and Fair Value (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Jun. 30, 2017USD ($)$ / sharesshares	Mar. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Sep. 30, 2016USD ($)$ / sharesshares	Jun. 30, 2016USD ($)$ / sharesshares	Mar. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2017USD ($)segment$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Net Income (loss) Per Common Share
Number of outstanding options not included in computation of Diluted EPS (in shares)									284,000	2,077,000	505,000,000
Numerator
Net income (loss) | $	$ 289,928	$ 53,716	$ 50,477	$ 34,786	$ (270,244)	$ 41,322	$ 40,244	$ 27,092	$ 428,907	$ (161,586)	$ 117,817
Denominator
Denominator for basic earnings per-share weighted average shares	51,811,000	51,833,000	51,751,000	51,820,000	51,757,000	51,627,000	51,418,000	51,218,000	51,804,000	51,505,000	51,077,000
Dilution due to stock options and restricted stock units (in shares)									1,296,000		748,000
Weighted average number of shares for diluted net income per common share	53,140,000	53,080,000	52,977,000	53,202,000	51,757,000	52,471,000	52,194,000	52,014,000	53,100,000	51,505,000	51,825,000
Basic earnings per-share (in dollars per share) | $ / shares	$ 5.60	$ 1.04	$ 0.98	$ 0.67	$ (5.22)	$ 0.80	$ 0.78	$ 0.53	$ 8.28	$ (3.14)	$ 2.31
Diluted earnings per-share (in dollars per share) | $ / shares	$ 5.46	$ 1.01	$ 0.95	$ 0.65	$ (5.22)	$ 0.79	$ 0.77	$ 0.52	$ 8.08	$ (3.14)	$ 2.27
Fair Value of Financial Instruments
Fair value of long-term debt | $	$ 2,698,400				$ 2,566,500				$ 2,698,400	$ 2,566,500
Total long-term debt | $	$ 2,712,350				$ 2,570,904				$ 2,712,350	$ 2,570,904
Segment Reporting
Number of operating segments | segment									3

Nature of Operations and Summ43

Nature of Operations and Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Long-term deferred income taxes payable	$ 419,020	$ 565,404
Retained Earnings (Accumulated Deficit)	1,516,957	1,103,751
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net deferred tax liabilities	900
Retained Earnings (Accumulated Deficit)	900
Income tax benefit	$ 5,400
Scenario, adjustment | Accounting Standards Update 2015-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net deferred tax liabilities		129,300
Long-term deferred income taxes payable		$ (129,300)

Segment Reporting (Details)

Segment Reporting (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)segmentaircraft	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Segment Reporting
Number of operating segments | segment									3
Operating revenues	$ 797,158	$ 831,936	$ 809,759	$ 765,415	$ 758,017	$ 799,776	$ 801,338	$ 762,075	$ 3,204,268	$ 3,121,206	$ 3,095,563
Operating expense									2,816,069	3,293,890	2,861,048
Depreciation and amortization expense									292,768	284,969	264,507
Special items					465,600					465,649
Interest expense									104,925	78,177	75,850
Segment profit (loss)									283,274	(250,861)	158,665
Identifiable intangible assets, other than goodwill	4,896				8,249				4,896	8,249	10,499
Total assets	5,458,279				5,007,966				5,458,279	5,007,966	4,781,984
Capital expenditures (including non-cash)									$ 689,398	1,159,001	715,089
CRJ 200
Segment Reporting
Number of aircraft lease to third party | aircraft									4
Special items										424,466
SkyWest Airlines
Segment Reporting
Operating revenues									$ 2,173,384	1,935,378	1,848,363
Operating expense									1,888,556	1,886,173	1,630,200
Depreciation and amortization expense									134,563	139,159	141,189
Special items										184,295
Interest expense									21,544	26,211	36,141
Segment profit (loss)									263,284	22,994	182,022
Total assets	2,228,930				2,250,276				2,228,930	2,250,276	2,300,388
Capital expenditures (including non-cash)									124,955	57,761	30,897
ExpressJet Airlines Inc
Segment Reporting
Operating revenues									790,942	1,044,828	1,169,923
Operating expense									819,343	1,339,569	1,192,070
Depreciation and amortization expense									51,982	83,935	86,382
Special items										281,354
Interest expense									4,127	6,773	12,091
Segment profit (loss)									(32,528)	(301,514)	(34,238)
Identifiable intangible assets, other than goodwill	4,896				8,249				4,896	8,249	10,499
Total assets	599,122				582,890				599,122	582,890	1,331,000
Capital expenditures (including non-cash)									14,278	15,396	24,679
ExpressJet Airlines Inc | CRJ 200
Segment Reporting
Special items									240,200
SkyWest Leasing
Segment Reporting
Operating revenues									239,942	141,000	77,277
Operating expense									108,170	68,148	38,778
Depreciation and amortization expense									106,223	61,875	36,936
Interest expense									79,254	45,193	27,618
Segment profit (loss)									52,518	27,659	10,881
Total assets	$ 2,630,227				$ 2,174,800				2,630,227	2,174,800	1,150,596
Capital expenditures (including non-cash)									$ 550,165	$ 1,085,844	$ 659,513

Long-term Debt (Details)

Long-term Debt (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)aircraft	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Debt Instrument [Line Items]
Total long-term debt	$ 2,712,350	$ 2,570,904
Current portion of long-term debt	(313,243)	(308,945)
Less long-term portion of unamortized debt issue cost, net	(21,761)	(21,908)
Long-term debt, net of current maturities and debt issue costs	2,377,346	2,240,051
Current portion of long-term debt	313,243	308,945
Less current portion of unamortized debt issue cost, net	(3,565)	(3,485)
Current portion of long-term debt, net of debt issue costs	$ 309,678	$ 305,460
Effective interest rate (as a percent)	3.90%	3.80%
Aggregate amounts of principal maturities of long-term debt
2,018	$ 313,243
2,019	315,753
2,020	284,998
2,021	272,470
2,022	280,360
Thereafter	1,245,526
Repayment of debt in cash		$ 16,500	$ 110,800
Total repayment of debt		18,400	145,400
Pre-tax gain		1,279	$ 33,660
Letters of credit	14,800	6,500
Current borrowing capacity	60,200	68,500
Letters of credit and surety bonds outstanding with various banks and surety institutions	$ 87,400	87,700
E 175
Debt Instrument [Line Items]
Number of new aircraft acquired | aircraft	21
Purchase price portion financed through debt issuance (as a percent)	85.00%
Purchase price portion paid with cash (as a percent)	15.00%
Notes payable to banks, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.91% to 3.43% through 2020, secured by aircraft
Debt Instrument [Line Items]
Total long-term debt	$ 34,905	63,408
Notes payable to banks, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.91% to 3.43% through 2020, secured by aircraft | Minimum
Debt Instrument [Line Items]
Interest rate (as a percent)	2.91%
Notes payable to banks, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.91% to 3.43% through 2020, secured by aircraft | Maximum
Debt Instrument [Line Items]
Interest rate (as a percent)	3.43%
Notes payable to a financing company, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.85% to 3.25% through 2021, secured by aircraft
Debt Instrument [Line Items]
Total long-term debt	$ 97,612	146,266
Notes payable to a financing company, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.85% to 3.25% through 2021, secured by aircraft | Minimum
Debt Instrument [Line Items]
Interest rate (as a percent)	2.85%
Notes payable to a financing company, due in semi-annual installments, variable interest based on LIBOR, or with interest rates ranging from 2.85% to 3.25% through 2021, secured by aircraft | Maximum
Debt Instrument [Line Items]
Interest rate (as a percent)	3.25%
Notes payable to banks, due in semi-annual installments plus interest at 6.06% to 6.51% through 2021, secured by aircraft
Debt Instrument [Line Items]
Total long-term debt	$ 63,090	86,052
Notes payable to banks, due in semi-annual installments plus interest at 6.06% to 6.51% through 2021, secured by aircraft | Minimum
Debt Instrument [Line Items]
Interest rate (as a percent)	6.06%
Notes payable to banks, due in semi-annual installments plus interest at 6.06% to 6.51% through 2021, secured by aircraft | Maximum
Debt Instrument [Line Items]
Interest rate (as a percent)	6.51%
Notes payable to a financing company, due in semi-annual installments plus interest at 5.78% to 6.23% through 2017, secured by aircraft
Debt Instrument [Line Items]
Total long-term debt		8,854
Notes payable to a financing company, due in semi-annual installments plus interest at 5.78% to 6.23% through 2017, secured by aircraft | Minimum
Debt Instrument [Line Items]
Interest rate (as a percent)	5.78%
Notes payable to a financing company, due in semi-annual installments plus interest at 5.78% to 6.23% through 2017, secured by aircraft | Maximum
Debt Instrument [Line Items]
Interest rate (as a percent)	6.23%
Notes payable to banks, due in monthly installments plus interest of 2.68% to 6.86% through 2025, secured by aircraft
Debt Instrument [Line Items]
Total long-term debt	$ 372,157	426,389
Notes payable to banks, due in monthly installments plus interest of 2.68% to 6.86% through 2025, secured by aircraft | Minimum
Debt Instrument [Line Items]
Interest rate (as a percent)	2.68%
Notes payable to banks, due in monthly installments plus interest of 2.68% to 6.86% through 2025, secured by aircraft | Maximum
Debt Instrument [Line Items]
Interest rate (as a percent)	6.86%
Notes payable to banks, due in monthly installments, plus interest at 4.16% to 6.05% through 2029, secured by aircraft
Debt Instrument [Line Items]
Total long-term debt	$ 49,001	8,998
Notes payable to banks, due in monthly installments, plus interest at 4.16% to 6.05% through 2029, secured by aircraft | Minimum
Debt Instrument [Line Items]
Interest rate (as a percent)	4.16%
Notes payable to banks, due in monthly installments, plus interest at 4.16% to 6.05% through 2029, secured by aircraft | Maximum
Debt Instrument [Line Items]
Interest rate (as a percent)	6.05%
Notes payable to banks, due in monthly installments, plus interest at 3.44% through 2019, secured by aircraft
Debt Instrument [Line Items]
Interest rate (as a percent)	3.44%
Total long-term debt		3,280
Notes payable to banks, due in quarterly installments plus interest at 3.39% to 4.73% through 2029, secured by aircraft
Debt Instrument [Line Items]
Total long-term debt	$ 2,085,822	1,806,981
Notes payable to banks, due in quarterly installments plus interest at 3.39% to 4.73% through 2029, secured by aircraft | Minimum
Debt Instrument [Line Items]
Interest rate (as a percent)	3.39%
Notes payable to banks, due in quarterly installments plus interest at 3.39% to 4.73% through 2029, secured by aircraft | Maximum
Debt Instrument [Line Items]
Interest rate (as a percent)	4.73%
Notes payable to banks, due in monthly installments, plus interest based on LIBOR at 3.54% through 2017, secured by aircraft
Debt Instrument [Line Items]
Interest rate (as a percent)	3.54%
Total long-term debt		4,666
Notes payable to banks due in monthly installments, interest based on LIBOR interest at 3.30% through 2019, secured by spare engines
Debt Instrument [Line Items]
Interest rate (as a percent)	3.30%
Total long-term debt	$ 9,763	16,010
Line of credit
Debt Instrument [Line Items]
Effective interest rate (as a percent)	4.10%
Aggregate amounts of principal maturities of long-term debt
Maximum borrowing capacity	$ 75,000	75,000
Amount outstanding	$ 0	$ 0
LIBOR | Line of credit
Debt Instrument [Line Items]
Basis spread on variable rate	2.50%

Income Taxes - Provision (Detai

Income Taxes - Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax provision (benefit):
Federal	$ 5,853	$ (3,801)	$ 3,801
State	180	111	1,035
Total current payable	6,033	(3,690)	4,836
Deferred tax provision (benefit):
Federal	(166,890)	(77,430)	66,430
State	20,133	(6,106)	5,239
Total deferred payable	(146,757)	(83,536)	71,669
Provision (benefit) for income taxes	$ (140,724)	$ (87,226)	$ 76,505

Income Taxes - Reconciliation (

Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statutory Federal income tax rate (as a percent)		35.00%
Reconciliation between the statutory federal income tax rate of 35% and the effective rate which is derived by dividing the provision for income taxes by income (loss) before income taxes
Computed provision (benefit) for income taxes at the statutory rate		$ 100,864	$ (87,084)	$ 68,013
State income tax provision (benefit), net of federal income tax benefit		7,778	(5,768)	5,416
Non-deductible expenses		3,230	3,552	3,641
Valuation allowance changes affecting the provision for income taxes		505	751	(899)
Excess tax benefits from share based compensation		(5,377)
Revaluation of net deferred tax liabilities for the Tax Act		(246,845)
Other, net		(879)	1,323	334
Provision (benefit) for income taxes		(140,724)	(87,226)	$ 76,505
Deferred tax assets:
Intangible Asset		(206)	4,983
Accrued benefits		31,651	48,482
Net operating loss carryforward		122,648	286,389
AMT credit carryforward		23,443	17,589
Deferred aircraft credits		53,870	60,415
Accrued reserves and other		26,853	47,906
Total deferred tax assets		258,259	465,764
Valuation allowance		(10,642)	(8,877)
Deferred tax liabilities:
Accelerated depreciation		(666,637)	(1,022,291)
Total deferred tax liabilities		(666,637)	(1,022,291)
Net deferred tax liability		$ (419,020)	$ (565,404)
Forecast
Statutory Federal income tax rate (as a percent)	21.00%

Income Taxes - Net Operating Lo

Income Taxes - Net Operating Losses and Tax Rates (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Net operating losses
Statutory Federal income tax rate (as a percent)	35.00%
Alternative minimum tax credit without expiration	$ 23,443	$ 17,589
Tax credit recovery period	4 years
Federal
Net operating losses
Operating loss carryforward	$ 491,400	763,900
Estimated effective tax rate on net operating losses	3.36
State
Net operating losses
Operating loss carryforward	$ 302,500	$ 469,200
Estimated effective tax rate on net operating losses	21

Commitments and Contingencies49

Commitments and Contingencies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)aircraft	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Future minimum rental payments required under operating leases
2,018	$ 142,157
2,019	104,297
2,020	121,119
2,021	112,657
2,022	75,981
Thereafter	160,621
Total future lease obligations	$ 716,832
Number of aircraft leased by the entity | aircraft	319
Minimum rental expense for airport station rents	$ 30,300	$ 31,400	$ 35,100

Commitments and Contingencies -

Commitments and Contingencies - Concentration Risks and Employees Under Collective Bargaining Agreements (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017USD ($)employee	Dec. 31, 2016USD ($)	Dec. 31, 2015
Concentration Risk and Significant Customers
Allowance for doubtful accounts | $		$ 157,000	$ 173,000
ExpressJet Delaware Mechanics | Subsequent event
Concentration Risk and Significant Customers
Labor agreement, contract extension term (in years)	1 year
Revenue from rights, concentration risk | Customer concentration risk | Delta, United, and Continental Combined
Concentration Risk and Significant Customers
Concentration risk (as a percent)		78.80%	85.40%	86.90%
Full-time equivalent number of employees
Concentration Risk and Significant Customers
Number of employees		16,300
Full-time equivalent number of employees | Unionized employees
Concentration Risk and Significant Customers
Concentration risk (as a percent)		22.00%
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Pilots
Concentration Risk and Significant Customers
Number of employees		669
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Flight Attendants
Concentration Risk and Significant Customers
Number of employees		552
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Flight Controllers
Concentration Risk and Significant Customers
Number of employees		25
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Mechanics
Concentration Risk and Significant Customers
Number of employees		102
Full-time equivalent number of employees | Unionized employees | Atlantic Southeast Stock Clerks
Concentration Risk and Significant Customers
Number of employees		29
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Pilots
Concentration Risk and Significant Customers
Number of employees		1,111
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Flight Attendants
Concentration Risk and Significant Customers
Number of employees		618
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Mechanics
Concentration Risk and Significant Customers
Number of employees		418
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Dispatchers
Concentration Risk and Significant Customers
Number of employees		22
Full-time equivalent number of employees | Unionized employees | ExpressJet Delaware Stock Clerks
Concentration Risk and Significant Customers
Number of employees		42

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Measurements
Marketable securities	$ 503,503	$ 409,898
Total Assets Measured at Fair Value	685,523	556,780
Recurring | Fair value
Fair Value Measurements
Marketable securities	503,503	409,898
Cash, Cash Equivalents and Restricted Cash	181,792	155,009
Total Assets Measured at Fair Value	685,295	564,907
Recurring | Fair value | Bonds and bond funds
Fair Value Measurements
Marketable securities	344,251	409,885
Recurring | Fair value | Commercial paper
Fair Value Measurements
Marketable securities	159,252	13
Recurring | Level 1
Fair Value Measurements
Cash, Cash Equivalents and Restricted Cash	181,792	155,009
Total Assets Measured at Fair Value	181,792	155,009
Recurring | Level 2
Fair Value Measurements
Marketable securities	503,503	409,898
Total Assets Measured at Fair Value	503,503	409,898
Recurring | Level 2 | Bonds and bond funds
Fair Value Measurements
Marketable securities	344,251	409,885
Recurring | Level 2 | Commercial paper
Fair Value Measurements
Marketable securities	$ 159,252	$ 13

Investment in Other Companies (

Investment in Other Companies (Details)	12 Months Ended
	Dec. 31, 2014
Trip Linhas Aereas
Investments in other companies
Annual rate of return used to calculate the put option price (as a percent)	20.00%

Special Items (Details)

Special Items (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Total Special items	$ 465,600		$ 465,649
Proceeds from settlement of residual value guarantee aircraft agreements			90,000
CRJ 200
Total Special items			424,466
ERJ 145
Total Special items			41,183
Estimated fair value	$ 41,200		41,200
SkyWest Airlines
Total Special items			184,295
Proceeds from settlement of residual value guarantee aircraft agreements		$ 90,000
ExpressJet Airlines Inc
Total Special items			$ 281,354
ExpressJet Airlines Inc | CRJ 200
Total Special items		$ 240,200

Capital Transactions - Preferre

Capital Transactions - Preferred Stock (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
Preferred Stock
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock outstanding (in shares)	0

Capital Transactions - Stock Co

Capital Transactions - Stock Compensation (Details) - USD ($)	May 04, 2010	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Performance period		90 days
Compensation expenses
Stock based compensation expense		$ 10,580,000	$ 7,568,000	$ 5,368,000
Director
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Granted (in shares)		22,617	42,624	36,950
Granted (in dollars per share)		$ 35.81	$ 14.78	$ 14.05
Number of shares
Granted (in shares)		22,617	42,624	36,950
Weighted Average Grant-Date Fair Value
Granted (in dollars per share)		$ 35.81	$ 14.78	$ 14.05
Maximum
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Award percentage		200.00%	150.00%
Minimum
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Award percentage		0.00%	0.00%
Stock options and restricted stock
Compensation expenses
Total unrecognized compensation cost					$ 10,600,000
Unrecognized compensation cost recognized over a weighted average period (in years)		1 year 8 months 12 days
Employee stock option
Share-Based Compensation
Options outstanding (in shares)		819,981	1,064,429	2,888,074	458,103	819,981
Compensation expenses
Period from grant date after which stock options become exercisable, minimum (in months)		6 months
Period from grant date within which incentive stock options are exercisable, maximum (in years)		7 years
Number of Options
Outstanding at the beginning of the period (in shares)		819,981	1,064,429	2,888,074
Granted (in shares)			206,021	267,433
Exercised (in shares)		(356,209)	(351,296)	(544,917)
Cancelled (in shares)		(5,669)	(99,173)	(1,546,161)
Outstanding at the end of the period (in shares)		458,103	819,981	1,064,429
Exercisable (in shares)					254,192	263,851
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)		$ 13.58	$ 13.64	$ 16.46
Granted (in dollars per share)			14.90	13.63
Exercised (in dollars per share)		13.36	14.17	14.68
Cancelled (in dollars per share)		14.33	14.90	18.53
Outstanding at the end of the period (in dollars per share)		$ 13.73	$ 13.58	$ 13.64
Exercisable (in dollars per share)					$ 13.17	$ 13.76
Weighted Average Remaining Contractual Term
Outstanding, Weighted Average Remaining Contractual Term (in years)		4 years	4 years 4 months 24 days
Exercisable, Weighted Average Remaining Contractual Term (in years)		3 years 4 months 24 days	2 years 9 months 18 days
Aggregate Intrinsic Value
Average intrinsic value of shares outstanding					$ 18,034,100	$ 18,756,900
Average intrinsic value of shares exercisable					$ 10,150,800	$ 5,985,500
Total intrinsic value of options exercised		$ 9,940,000	$ 4,250,000	$ 1,800,000
Non-vested stock options
Non-vested shares at beginning of year (in shares)		556,130
Granted (in shares)			206,021	267,433
Vested (in shares)		(346,550)
Cancelled (in shares)		(5,669)
Non-vested shares at end of year (in shares)		203,911	556,130
Weighted Average Grant-Date Fair Value
Non-vested shares at beginning of year (in dollars per share)		$ 4.86
Vested (in dollars per share)		4.67
Cancelled (in dollars per share)		5.14
Non-vested shares at end of year (in dollars per share)		$ 5.17	$ 4.86
Performance share units
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Granted (in shares)		119,315	183,577	222,583
Granted (in dollars per share)		$ 35.81	$ 14.89	$ 13.61
Performance period		3 years
Number of shares
Nonvested shares at the beginning of the period (in shares)		363,993	202,829
Granted (in shares)		119,315	183,577	222,583
Cancelled (in shares)		(14,732)	(22,413)	(19,754)
Nonvested shares at the end of the period (in shares)		468,576	363,993	202,829
Weighted Average Grant-Date Fair Value
Nonvested shares at the beginning of the period (in dollars per share)		$ 14.23	$ 13.62
Granted (in dollars per share)		35.81	14.89	$ 13.61
Cancelled (in dollars per share)		15	14.16	13.51
Nonvested shares at the end of the period (in dollars per share)		$ 19.70	$ 14.23	$ 13.62
Restricted stock units
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Granted (in shares)		160,137	384,148	408,163
Granted (in dollars per share)		$ 35.81	$ 14.81	$ 13.57
Number of shares
Nonvested shares at the beginning of the period (in shares)		926,931	809,299	723,176
Granted (in shares)		160,137	384,148	408,163
Vested (in shares)		(230,903)	(215,146)	(215,856)
Cancelled (in shares)		(40,575)	(51,370)	(106,184)
Nonvested shares at the end of the period (in shares)		815,590	926,931	809,299
Weighted Average Grant-Date Fair Value
Nonvested shares at the beginning of the period (in dollars per share)		$ 13.65	$ 13.13	$ 12.70
Granted (in dollars per share)		35.81	14.81	13.57
Vested (in dollars per share)		12.01	13.29	13.06
Cancelled (in dollars per share)		15.78	13.72	13.52
Nonvested shares at the end of the period (in dollars per share)		$ 18.35	$ 13.65	$ 13.13
Long Term Incentive Plan 2010
Share-Based Compensation
Number of shares authorized	5,150,000
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Vesting period			3 years	3 years
Long Term Incentive Plan 2010 | Employee stock option
Share-Based Compensation
Minimum incentive stock option exercise price, expressed as a percentage of common stock grant date market value	100.00%
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Expected annual dividend rate (as a percent)			1.08%	1.18%
Risk-free interest rate (as a percent)			1.15%	1.62%
Average expected life (years)			5 years 8 months 12 days	5 years 8 months 12 days
Expected volatility of common stock (as a percent)			0.412%	0.401%
Forfeiture rate (as a percent)			0.00%	0.00%
Weighted average fair value of option grants			$ 5.27	$ 4.75
Number of Options
Granted (in shares)			206,021	267,433
Non-vested stock options
Granted (in shares)			206,021	267,433
Weighted Average Grant-Date Fair Value
Granted (in dollars per share)			$ 5.27	$ 4.75
Long Term Incentive Plan 2010 | Restricted stock units
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Vesting period		3 years
Granted (in dollars per share)		$ 35.81
Weighted Average Grant-Date Fair Value
Granted (in dollars per share)		$ 35.81
Long Term Incentive Plan 2010 | Restricted stock units | Director
Assumptions used to determine value of the shares purchased under the stock purchase plan using Black-Scholes option pricing model
Granted (in shares)		160,137
Number of shares
Granted (in shares)		160,137

Capital Transactions - Informat

Capital Transactions - Information About Stock Options Outstanding (Details)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
$8.00 to $12.99
Stock options, exercise price
Exercise price range, low end of range (in dollars per share)	$ 8
Exercise price range, high end of range (in dollars per share)	$ 12.99
Options Outstanding
Number of options outstanding (in shares) | shares	79,990
Options outstanding, Weighted Average Remaining Contractual Life	3 years 1 month 6 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 12.06
Options Exercisable
Number of options Exercisable (in shares) | shares	79,990
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 12.06
$13.00 to $14.99
Stock options, exercise price
Exercise price range, low end of range (in dollars per share)	13
Exercise price range, high end of range (in dollars per share)	$ 14.99
Options Outstanding
Number of options outstanding (in shares) | shares	371,480
Options outstanding, Weighted Average Remaining Contractual Life	4 years 2 months 12 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 14.02
Options Exercisable
Number of options Exercisable (in shares) | shares	173,481
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 13.67
$15.00 to $19.00
Stock options, exercise price
Exercise price range, low end of range (in dollars per share)	15
Exercise price range, high end of range (in dollars per share)	$ 19
Options Outstanding
Number of options outstanding (in shares) | shares	6,633
Options outstanding, Weighted Average Remaining Contractual Life	4 years 9 months 18 days
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 17.77
Options Exercisable
Number of options Exercisable (in shares) | shares	721
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 15.03
$8.00 to $19.00
Stock options, exercise price
Exercise price range, low end of range (in dollars per share)	8
Exercise price range, high end of range (in dollars per share)	$ 19
Options Outstanding
Number of options outstanding (in shares) | shares	458,103
Options outstanding, Weighted Average Remaining Contractual Life	4 years
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 13.73
Options Exercisable
Number of options Exercisable (in shares) | shares	254,192
Options Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 13.17

Retirement Plans and Employee57

Retirement Plans and Employee Stock Purchase Plans - Retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SkyWest Plan
Retirement Plans
Service period required to be completed to be eligible to participate in plan	90 days
Required age for an employee to be eligible to participate in plan	18 years
Percentage of employer matching contribution based on length of service	100.00%
Minimum benefit plan percentage of participants compensation eligible for employer matching contribution based on position and years of service	2.00%
Maximum benefit plan percentage of participants compensation eligible for employer matching contribution based on position and years of service	7.00%
Company's combined contributions	$ 26.1	$ 23.2	$ 20.4
Atlantic Southeast and the ExpressJet Plans
Retirement Plans
Service period required to be completed to be eligible to participate in plan	90 days
Required age for an employee to be eligible to participate in plan	18 years
Company's combined contributions	$ 17.8	$ 21	$ 24
Maximum percentage of participant's total compensation eligible for employer matching contribution	8.00%
Atlantic Southeast Plan
Retirement Plans
Percentage of vesting for plan participants' elective deferrals and rollover amounts	100.00%
Atlantic Southeast Plan | Minimum
Retirement Plans
Percentage of vesting of company matching contribution based on length of service	10.00%
Atlantic Southeast Plan | Maximum
Retirement Plans
Percentage of vesting of company matching contribution based on length of service	100.00%

Retirement Plans and Employee58

Retirement Plans and Employee Stock Purchase Plans - Employee Stock Purchase Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Stock Purchase Plans
Service period required to be completed for an employee to be eligible to participate in plan, minimum	90 days
Ownership interest in Company common stock to disqualify employee from participation in plan, maximum (as a percent)	5.00%
Maximum percentage of base salary which can be contributed by the employees	15.00%
Maximum amount of base salary which can be contributed annually by the employees	$ 25,000
Discount rate at which common stock can be purchased by the plan participant (as a percent)	5.00%
Summary of purchases made under the 2010 and 1995 Employee Stock Purchase Plans
Number of shares purchased	88,362	151,531	254,098
Average price of shares purchased (in dollars per share)	$ 33.96	$ 20.87	$ 13.50
2009 Stock Purchase Plan
Summary of purchases made under the 2010 and 1995 Employee Stock Purchase Plans
Stock based compensation expense	$ 0	$ 0	$ 0

Stock Repurchase (Details)

Stock Repurchase (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Repurchase
Common stock authorized for repurchase, maximum (in shares)		100
Stock repurchase program year	3 years
Common stock remaining number of shares authorized to repurchase		80
Common stock repurchased (in shares)		0.5	0	1.3
Common stock repurchased, value		$ 20,000		$ 18,700
Weighted average price per share of common stock (in dollars per share)		$ 41.36		$ 14.98
Payment of income tax obligation on employee equity awards		$ (5,080)

Related-Party Transactions (Det

Related-Party Transactions (Details)	12 Months Ended
	Dec. 31, 2017USD ($)
Affiliated entity
Related Party Transactions
Purchase from related party	$ 198,000

Quarterly Financial Data (Una61

Quarterly Financial Data (Unaudited) (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Jun. 30, 2017USD ($)$ / sharesshares	Mar. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesitemshares	Sep. 30, 2016USD ($)$ / sharesshares	Jun. 30, 2016USD ($)$ / sharesshares	Mar. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Quarterly Financial Data (Unaudited)
Operating revenues	$ 797,158	$ 831,936	$ 809,759	$ 765,415	$ 758,017	$ 799,776	$ 801,338	$ 762,075	$ 3,204,268	$ 3,121,206	$ 3,095,563
Operating income (loss)	92,939	112,369	106,596	76,295	(404,464)	85,834	84,137	61,809	388,199	(172,684)	234,515
Net income (loss)	$ 289,928	$ 53,716	$ 50,477	$ 34,786	$ (270,244)	$ 41,322	$ 40,244	$ 27,092	$ 428,907	$ (161,586)	$ 117,817
Net income (loss) per common share:
Basic (in dollars per share) | $ / shares	$ 5.60	$ 1.04	$ 0.98	$ 0.67	$ (5.22)	$ 0.80	$ 0.78	$ 0.53	$ 8.28	$ (3.14)	$ 2.31
Diluted (in dollars per share) | $ / shares	$ 5.46	$ 1.01	$ 0.95	$ 0.65	$ (5.22)	$ 0.79	$ 0.77	$ 0.52	$ 8.08	$ (3.14)	$ 2.27
Weighted average common shares:
Basic (in shares) | shares	51,811	51,833	51,751	51,820	51,757	51,627	51,418	51,218	51,804	51,505	51,077
Diluted (in shares) | shares	53,140	53,080	52,977	53,202	51,757	52,471	52,194	52,014	53,100	51,505	51,825
Revaluation of deferred tax liablity									$ 246,800
Special Charge					$ 465,600					$ 465,649
Number of seats on aircraft | item					50

SCHEDULE II_VALUATION AND QUA62

SCHEDULE II—VALUATION AND QUALIFYING ACCOUNTS (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2016USD ($)item	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Year		$ 40,670	$ 14,120	$ 11,914
Additions Charged to Costs and Expenses			26,564	2,345
Deductions		(23,415)	(14)	(139)
Balance at End of Year	$ 40,670	17,255	40,670	14,120
Number of seats on aircraft | item	50
Allowance for inventory obsolescence
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Year		40,497	13,933	11,588
Additions Charged to Costs and Expenses			26,564	2,345
Deductions		(23,399)
Balance at End of Year	$ 40,497	17,098	40,497	13,933
Allowance for doubtful accounts receivable
VALUATION AND QUALIFYING ACCOUNTS
Balance at Beginning of Year		173	187	326
Deductions		(16)	(14)	(139)
Balance at End of Year	$ 173	$ 157	$ 173	$ 187