Carrying amount of assets sold under agreements to repurchase when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under repurchase agreements exceeds 10 percent of total assets.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(A)(i))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

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

- Definition

Describes the periods of time over which an entity anticipates to receive utility from its property, plant and equipment (that is, the periods of time over which an entity allocates the initial cost of its property, plant and equipment).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 35
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68071081&loc=d3e1205-110223

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790

+ Details

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

- Definition

Stated as a percentage, the estimated or actual value of the asset at the end of its useful life or when it is no longer serviceable (cannot be used for its original purpose) divided by its [historical] capitalized cost.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentSalvageValuePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=futu_ComputersAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_FurnitureAndFixturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_OfficeEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_VehiclesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=srt_OfficeBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment, net (Details) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020 HKD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 HKD ($)
PROPERTY AND EQUIPMENT, NET
Assets Sold under Agreements to Repurchase, Carrying Amount	$ 5,453,037	$ 703,309	$ 1,590
Computers and equipment
PROPERTY AND EQUIPMENT, NET
Residual rate (as a percent)	5.00%	5.00%
Computers and equipment \| Minimum
PROPERTY AND EQUIPMENT, NET
Estimated useful lives	P3Y
Computers and equipment \| Maximum
PROPERTY AND EQUIPMENT, NET
Estimated useful lives	P5Y
Furniture and fixtures
PROPERTY AND EQUIPMENT, NET
Residual rate (as a percent)	5.00%	5.00%
Furniture and fixtures \| Minimum
PROPERTY AND EQUIPMENT, NET
Estimated useful lives	P3Y
Furniture and fixtures \| Maximum
PROPERTY AND EQUIPMENT, NET
Estimated useful lives	P5Y
Office equipment
PROPERTY AND EQUIPMENT, NET
Residual rate (as a percent)	5.00%	5.00%
Office equipment \| Minimum
PROPERTY AND EQUIPMENT, NET
Estimated useful lives	P3Y
Office equipment \| Maximum
PROPERTY AND EQUIPMENT, NET
Estimated useful lives	P5Y
Vehicle
PROPERTY AND EQUIPMENT, NET
Estimated useful lives	P5Y
Residual rate (as a percent)	5.00%	5.00%
Office building
PROPERTY AND EQUIPMENT, NET
Estimated useful lives	P30Y
Residual rate (as a percent)	5.00%	5.00%