The amount of contra-asset as a reduction to maintenance expense recognized in the statements of operations

No definition available.

Name:	sncy_ContraAssetsAsReductionToMaintenanceExpense
Namespace Prefix:	sncy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of contra assets outstanding as on the balance sheet date

+ References

No definition available.

+ Details

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

- Definition

The amount of decrease in contra assets relating to purchase of aircrafts previously leased.

+ References

No definition available.

+ Details

Name:	sncy_DecreaseInContraAssetsRelatingToPurchaseOfAircraftsPreviouslyLeased
Namespace Prefix:	sncy_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of increase (decrease) in contra assets during the period.

+ References

No definition available.

+ Details

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

- Definition

The amount of maintenance reserve payments expensed during the period.

+ References

No definition available.

+ Details

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

- Definition

Number of aircrafts previously under operating leases which were purchased during the period.

+ References

No definition available.

+ Details

Name:	sncy_NumberOfPurchasedAircraftsPreviouslyUnderOperatingLeases
Namespace Prefix:	sncy_
Data Type:	xbrli:integerItemType
Balance Type:	na
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_LesseeLeaseDescriptionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

LEASES - Additional disclosures (Details) $ in Thousands	3 Months Ended			9 Months Ended	12 Months Ended
LEASES - Additional disclosures (Details) $ in Thousands	Mar. 31, 2021 USD ($) aircraft	Mar. 31, 2020 USD ($)	Apr. 10, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 USD ($) aircraft	Dec. 31, 2019 USD ($)
LEASES
Maintenance reserve payments expensed			$ 6,003	$ 12,781	$ 8,691	$ 18,584
Number of aircrafts previously under operating leases \| aircraft	5				2
Aircraft maintenance deposits contra assets
LEASES
Remaining balance of the contra-asset	$ 26,512				$ 36,729	43,844
Reduction in the contra-asset					7,115
Purchase of number of aircrafts previously leased	$ 9,880				$ 5,624
Number of aircrafts previously under operating leases \| aircraft	5				2
Contra-asset as a reduction to Maintenance expense	$ 0	$ 425		$ 6,516	$ 1,402	$ 12,263