The amount of cash refund to customers due to COVID-19 related flight cancellations.

No definition available.

Name:	sncy_CashRefundToCustomersDueToCovid19RelatedFlightCancellations
Namespace Prefix:	sncy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The contract assets primarily relate to cost incurred to get this number of cargo aircraft ready for service.

+ References

No definition available.

+ Details

Name:	sncy_ContractAssetsPrimarilyRelateToCostIncurredToGetCargoAircraftsReadyForServiceNumber
Namespace Prefix:	sncy_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of outstanding contract with customer liability due to COVID-19 extensions.

+ References

No definition available.

+ Details

Name:	sncy_ContractWithCustomersLiabilityDueToCovid19Extensions
Namespace Prefix:	sncy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of outstanding contract with customer liability due to gift certificates.

+ References

No definition available.

+ Details

Name:	sncy_ContractWithCustomersLiabilityDueToGiftCertificates
Namespace Prefix:	sncy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the threshold period in which tickets can be booked in advance.

+ References

No definition available.

+ Details

Name:	sncy_ThresholdPeriodInWhichTicketsCanBeBookedInAdvance
Namespace Prefix:	sncy_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maintenance costs incurred and directly related to services rendered by an entity during the reporting period. Includes the cost of inspections and repairs, materials and routine maintenance costs for all aircraft and engines.

+ References

No definition available.

+ Details

Name:	us-gaap_AircraftMaintenanceMaterialsAndRepairs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130531-203044

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130533-203044

+ Details

Name:	us-gaap_ContractWithCustomerAssetNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130531-203044

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130532-203044

+ Details

Name:	us-gaap_ContractWithCustomerLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

+ Details

Name:	us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DisaggregationOfRevenueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=sncy_AirTrafficLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=sncy_LoyaltyProgramLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=sncy_AmazonDeferredStartUpCostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=sncy_CostsToFulfillContractWithAmazonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_PassengerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

REVENUE - Contract Balances (Details) $ in Thousands	3 Months Ended			9 Months Ended	12 Months Ended
REVENUE - Contract Balances (Details) $ in Thousands	Mar. 31, 2021 USD ($) aircraft	Mar. 31, 2020 USD ($)	Apr. 10, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 USD ($) aircraft	Dec. 31, 2019 USD ($)
REVENUE
Maintenance expense	$ 9,210	$ 6,478	$ 9,508	$ 15,491	$ 27,416	$ 35,286
Total Contract Liabilities	120,517				128,383	141,185
Air Traffic Liabilities
REVENUE
Total Contract Liabilities	$ 94,733				$ 101,075	116,660
Threshold period in which tickets can be booked in advance	12 months				12 months
Cash refund to customers						4,502
Customer liability outstanding					$ 1,045
Gift certificates					245
Loyalty Program Liabilities
REVENUE
Total Contract Liabilities	$ 20,774	22,321		$ 23,950	22,069	22,892
Revenue recognized	2,152	$ 2,206			4,838	12,408
Amazon Deferred Up-front Payment
REVENUE
Total Contract Liabilities	$ 5,010				5,240	$ 1,633
Revenue recognized					$ 393
Costs to fulfill contract with Amazon
REVENUE
Number of cargo aircraft \| aircraft	12				12
Maintenance expense	$ 138				$ 271
Contract Assets	3,312				3,614
Passenger \| Air Traffic Liabilities
REVENUE
Revenue recognized	$ 60,039				$ 110,868