Dividends, Common Stock, Stock, Issuable

No definition available.

Name:	bsy_DividendsCommonStockStockIssuable
Namespace Prefix:	bsy_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of contributions made by employer into fund established for purposes of making future disbursement to individual in accordance with deferred compensation arrangement.

+ References

No definition available.

+ Details

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

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

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

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

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis=us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTaxStatusAxis=us-gaap_NonqualifiedPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=bsy_PriorToJanuary2016AwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=bsy_AfterJanuary2016AwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=bsy_ShareBasedPaymentArrangementTrancheFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=bsy_ShareBasedPaymentArrangementTrancheFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Retirement Plans - Narrative (Details) - Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Defined Contribution Plan Disclosure [Line Items]
Deferred compensation liability, current and noncurrent	$ 2,757,000		$ 2,591,000
Nonqualified Plan
Defined Contribution Plan Disclosure [Line Items]
Contributions by employer	$ 0	$ 0
Phantom shares issuable (in shares)	30,076,143		30,590,955
Share-based Payment Arrangement, Tranche One \| Nonqualified Plan \| Prior to January 2016 Awards
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage	20.00%
Share-based Payment Arrangement, Tranche One \| Nonqualified Plan \| After January 2016 Awards
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage	100.00%
Share-based Payment Arrangement, Tranche Two \| Nonqualified Plan \| Prior to January 2016 Awards
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage	20.00%
Share-based Payment Arrangement, Tranche Three \| Nonqualified Plan \| Prior to January 2016 Awards
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage	20.00%
Share-Based Payment Arrangement, Tranche Four \| Nonqualified Plan \| Prior to January 2016 Awards
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage	20.00%
Share-Based Payment Arrangement, Tranche Five \| Nonqualified Plan \| Prior to January 2016 Awards
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage	20.00%