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	%	30	%
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	0	%	No Change
Leasehold improvements	Shorter of 15 years or lease term	No Change	0	%	No Change
Buildings	20 - 39.5 years	No Change	0	%	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 Dates
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 Dates
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 Dates
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