Effective date of new enterprise income tax law. .

No definition available.

Name:	bz_EffectiveDateOfNewEnterpriseIncomeTaxLaw
Namespace Prefix:	bz_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

IncomeTaxDisclosure [Line items]

+ References

No definition available.

+ Details

Name:	bz_IncometaxdisclosureLineItems
Namespace Prefix:	bz_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of additional deduction on qualified research and development expenses.

+ References

No definition available.

+ Details

Name:	bz_PercentageOfAdditionalDeductionOnQualifiedResearchAndDevelopmentExpenses
Namespace Prefix:	bz_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of tax deduction on qualified research and development expenses.

+ References

No definition available.

+ Details

Name:	bz_PercentageOfTaxDeductionOnQualifiedResearchAndDevelopmentExpenses
Namespace Prefix:	bz_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of value added tax rate in super deduction.

+ References

No definition available.

+ Details

Name:	bz_PercentageOfValueAddedTaxRateInSuperDeduction
Namespace Prefix:	bz_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Preferential income tax rate.

+ References

No definition available.

+ Details

Name:	bz_PreferentialIncomeTaxRate
Namespace Prefix:	bz_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Tax losses carryforward expiration period.

+ References

No definition available.

+ Details

Name:	bz_TaxLossesCarryforwardExpirationPeriod
Namespace Prefix:	bz_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Uniform tax rate for foreign investment enterprises and domestic.

+ References

No definition available.

+ Details

Name:	bz_UniformTaxRateForForeignInvestmentEnterprisesAndDomestic
Namespace Prefix:	bz_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Value added tax rate.

+ References

No definition available.

+ Details

Name:	bz_ValueAddedTaxRate
Namespace Prefix:	bz_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 6.I.Fact.4)
-URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32687-109319

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32559-109319

+ Details

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

- Details

Name:	bz_ApplicabilityOfPreferentialTaxRateAxis=bz_QualifiedHighAndNewTechnologyEnterpriseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	bz_PreferentialTaxRatePeriodAxis=bz_ExpireInTwoThousandAndTwentyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	bz_ValueAddedTaxInSuperDeductionPeriodAxis=bz_AprilOneTwoThousandAndNineteenToDecemberThirtyOneTwoThousandAndTwentyOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityNameAxis=us-gaap_CaliforniaFranchiseTaxBoardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_CN
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	bz_LawOfEnterpriseAxis=bz_NewEnterpriseIncomeTaxLawMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Taxation - Additional Information (Detail) - CNY (¥) ¥ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
IncomeTaxDisclosure [Line Items]
Value added tax rate	6.00%
Statutory income tax rate	25.00%	25.00%	25.00%
Accumulated tax losses	¥ 308.9
Qualified High and New Technology Enterprise [Member]
IncomeTaxDisclosure [Line Items]
Tax losses carryforward expiration period	10 years
Qualified High and New Technology Enterprise [Member] \| Expire in Two Thousand And Twenty Two [Member]
IncomeTaxDisclosure [Line Items]
Preferential income tax rate	15.00%
April 1, 2019 to December 31, 2021 [Member]
IncomeTaxDisclosure [Line Items]
Percentage of value added tax rate in super deduction	10.00%
United States [Member]
IncomeTaxDisclosure [Line Items]
Statutory income tax rate	21.00%	21.00%	21.00%
United States [Member] \| California corporate franchise tax [Member]
IncomeTaxDisclosure [Line Items]
Statutory income tax rate	8.84%	8.84%	8.84%
Tax losses carryforward expiration period	20 years
China [Member]
IncomeTaxDisclosure [Line Items]
Tax losses carryforward expiration period	5 years
Percentage of tax deduction on qualified research and development expenses	175.00%
Percentage of additional deduction on qualified research and development expenses	75.00%
China [Member] \| Qualified High and New Technology Enterprise [Member]
IncomeTaxDisclosure [Line Items]
Preferential income tax rate	15.00%
China [Member] \| New Enterprise Income Tax Law [Member]
IncomeTaxDisclosure [Line Items]
Uniform tax rate for foreign investment enterprises and domestic	25.00%
Effective date of new enterprise income tax law	Jan. 01, 2008